As I've been playing, I've noticed that these two realms actually have some significant problems that stop them from being effective. Keep in mind I'm mostly talking mono realm play.
Chaos:
Chaos' whole deal is to win with strong combat spells. And that works on Rare and above, when you get spells like Flame Strike, spellcasting units like Efreet, and enough casting skill to spam stuff like Lightning Bolt and Warp Lightning. But before that, Chaos' options are very limited. Fire Bolt is good sure.. but in the early game you can generally only cast it 2 times in combat. Hell Hounds are a bad joke, they are okay as a filler summon but their frailty stops them from being very useful. Barring Flame Blade and Wall of Fire, most other common spells are simply not very useful, with the notable exception of Warp Creature when combined with other realms. So to compensate, you'd think the Uncommon spells are better, right? Well... sort of.
Gargoyles are good anti personnel units, but against other uncommon summons, their attack is a bad joke. Chimeras are powerful attackers, but greatly gimped by their high research costs, low resistance, and being forced into melee combat, especially at an unremarkable speed of 3. Fire Giants are thoroughly mediocre, though they atleast are a ranged magical attacker that don't die like flies when hurt. Given the problems with their units, you would think the buffs and combat damage spells are better. And.. they are, kind of.
Chaos Channels is a good buff, but honestly, it's weaker than Life common spells, the only real advantage over them being that it provides non dispellable effects and allows units to counter flying enemies reasonably well. It works much better with Nature Uncommon and Rare spells. Immolation is fairly situational, mostly useful on Gargoyles, who are already likely used as anti personnel units. Lightning Bolt is good but generally less cost efficient than Fire Bolt. Fireball is a good side spell to Fire Bolt, though its value is diminished since all magicians have it by default. Mystic Surge is a fairly situational risky spell that does fit the realm but doesn't solve the problems with it, and Fate Mastery is basically the Uncommon version of Warp Creature: great in combo realms, kind of meh in Chaos itself.
I understand that Chaos is supposed to bide time and build up power before unleashing it on the world. But I think waiting still Rare tier is a bit much to ask for. Making the Uncommon tier more versatile so that Chaos can reasonably survive and be in a good position to hurl its Rares would be a good idea imo.
There IS one thing Chaos is good at before Rare tier: giving some nifty immunities to heroes. While Chaos' hero support is generally worse than Life, having immunity to Fire and Cold, cutting down the impact of armor piercing attacks, and gaining Chaos' spells innately along with enchantments from Chaos Channel is very worthwhile.
Death:
Death is fairly one dimensional, and not in ways you would expect. There are games where you can simply steamroll enemies since you brought lots of ghouls against unprepared garrisons early, and then there are games where Death is stuck in a quandry since none of their options are really effective. In particular, I think what hurts Death the most is that their units are too specialized. Ghouls are great against many regular units, but anything with high enough resist or Poison Immunity simply shuts them down. Shadow Demons are menacing as a stack, being a bunch of regenerating wraithformed flyers with lots of shots.. but they simply get destroyed by their counters. And those counters are fairly abundant, being commonplace in the Nature and Life realms. When their units don't work, Death only has regular units and combat spells to fall back on. And both of these have problems.
Death is incredibly bad at buffing, the only relevant buff being cloak of fear for the most part. This means that regular units are absurdly bad with Death; only tanky units can afford to get into melee range against most garrisons for the cloak to take effect. As for combat spells.. they generally suffer from either having bad resistance modifiers or being limited by unit type or not being readily effective. Black Sleep at -2 would be good except that you still need units in range to kill it. Zombies are alright but easily get cut down to ribbons by any competent army. Life Drain is incredibly wimpy when cast on targets having above five resist.. which is a lot of them. Mislead is very situational, and is further hurt by only being able to affect regular units.
Things do improve at Uncommon. Blood Lust is actually a fairly nifty buff, since it grants Illusion, Cold, and Death Immunity, all of which are quite useful. Of course, losing combat experience and the ability to heal is a downside, but it's not that problematic on regular troops, who are intended to be mass produced. Syphon Life is basically what Life Drain should've been. Reaper Slash is good, though nothing special as far as direct damage spells go. Possession is limited greatly by only targeting regular units, though atleast it does its job well. Black Prayer is the clear winner here, allowing the resistance based spells to generally function better. Oddly it doesn't do much for Shadow Demons, Death's best uncommon summon. Lycanthropy produces good but unremarkable units; it really feels like a spell that should be in the Common tier. Mana Leak is situationally powerful - draining ranged magical units of ammo every turn is good, but on the offensive they will get to throw a shot first anyway. Similarly Night Stalker is situationally powerful, they can assassinate a lot of things with Cloak of Fear and Black Prayer, but all it takes is a True Sight and/or some good high resist units to make them impotent.
Ultimately, what makes Death hard to play is that their summons are generally specialized, they can't buff their regular units well enough to cover the gaps, and even their spells do not fill them. Death also has a major power gap between Shadow Demons and Death Knights/Demon Lords - Vampires and Wraiths are too vulnerable to really work as the cornerstone of Death armies in Rare tier. This means that Death infact needs heroes even more than Life or Sorcery - the realms intended to buff heroes. This is quite counterintuitive, considering that Death has little to offer a hero outside of Wraith Form for stopping Web/Crack's Call, and Vampiric to heal themselves and raise undead. Egoism is okay for atleast getting heroes levels faster, and Stealth is nifty for scouting lairs. Dark Force seems way too risky to rely on, especially since heroes generally don't get much HP until they reach high levels, and enemies tend to stall when they can't win.
My suggestion for Death is honestly similar to what I suggested for Chaos: make it more versatile at the Uncommon tier. It's a shame that Death is supposed to be strong in the early game, yet can easily run into roadblocks they can't deal with.
Chaos:
Chaos' whole deal is to win with strong combat spells. And that works on Rare and above, when you get spells like Flame Strike, spellcasting units like Efreet, and enough casting skill to spam stuff like Lightning Bolt and Warp Lightning. But before that, Chaos' options are very limited. Fire Bolt is good sure.. but in the early game you can generally only cast it 2 times in combat. Hell Hounds are a bad joke, they are okay as a filler summon but their frailty stops them from being very useful. Barring Flame Blade and Wall of Fire, most other common spells are simply not very useful, with the notable exception of Warp Creature when combined with other realms. So to compensate, you'd think the Uncommon spells are better, right? Well... sort of.
Gargoyles are good anti personnel units, but against other uncommon summons, their attack is a bad joke. Chimeras are powerful attackers, but greatly gimped by their high research costs, low resistance, and being forced into melee combat, especially at an unremarkable speed of 3. Fire Giants are thoroughly mediocre, though they atleast are a ranged magical attacker that don't die like flies when hurt. Given the problems with their units, you would think the buffs and combat damage spells are better. And.. they are, kind of.
Chaos Channels is a good buff, but honestly, it's weaker than Life common spells, the only real advantage over them being that it provides non dispellable effects and allows units to counter flying enemies reasonably well. It works much better with Nature Uncommon and Rare spells. Immolation is fairly situational, mostly useful on Gargoyles, who are already likely used as anti personnel units. Lightning Bolt is good but generally less cost efficient than Fire Bolt. Fireball is a good side spell to Fire Bolt, though its value is diminished since all magicians have it by default. Mystic Surge is a fairly situational risky spell that does fit the realm but doesn't solve the problems with it, and Fate Mastery is basically the Uncommon version of Warp Creature: great in combo realms, kind of meh in Chaos itself.
I understand that Chaos is supposed to bide time and build up power before unleashing it on the world. But I think waiting still Rare tier is a bit much to ask for. Making the Uncommon tier more versatile so that Chaos can reasonably survive and be in a good position to hurl its Rares would be a good idea imo.
There IS one thing Chaos is good at before Rare tier: giving some nifty immunities to heroes. While Chaos' hero support is generally worse than Life, having immunity to Fire and Cold, cutting down the impact of armor piercing attacks, and gaining Chaos' spells innately along with enchantments from Chaos Channel is very worthwhile.
Death:
Death is fairly one dimensional, and not in ways you would expect. There are games where you can simply steamroll enemies since you brought lots of ghouls against unprepared garrisons early, and then there are games where Death is stuck in a quandry since none of their options are really effective. In particular, I think what hurts Death the most is that their units are too specialized. Ghouls are great against many regular units, but anything with high enough resist or Poison Immunity simply shuts them down. Shadow Demons are menacing as a stack, being a bunch of regenerating wraithformed flyers with lots of shots.. but they simply get destroyed by their counters. And those counters are fairly abundant, being commonplace in the Nature and Life realms. When their units don't work, Death only has regular units and combat spells to fall back on. And both of these have problems.
Death is incredibly bad at buffing, the only relevant buff being cloak of fear for the most part. This means that regular units are absurdly bad with Death; only tanky units can afford to get into melee range against most garrisons for the cloak to take effect. As for combat spells.. they generally suffer from either having bad resistance modifiers or being limited by unit type or not being readily effective. Black Sleep at -2 would be good except that you still need units in range to kill it. Zombies are alright but easily get cut down to ribbons by any competent army. Life Drain is incredibly wimpy when cast on targets having above five resist.. which is a lot of them. Mislead is very situational, and is further hurt by only being able to affect regular units.
Things do improve at Uncommon. Blood Lust is actually a fairly nifty buff, since it grants Illusion, Cold, and Death Immunity, all of which are quite useful. Of course, losing combat experience and the ability to heal is a downside, but it's not that problematic on regular troops, who are intended to be mass produced. Syphon Life is basically what Life Drain should've been. Reaper Slash is good, though nothing special as far as direct damage spells go. Possession is limited greatly by only targeting regular units, though atleast it does its job well. Black Prayer is the clear winner here, allowing the resistance based spells to generally function better. Oddly it doesn't do much for Shadow Demons, Death's best uncommon summon. Lycanthropy produces good but unremarkable units; it really feels like a spell that should be in the Common tier. Mana Leak is situationally powerful - draining ranged magical units of ammo every turn is good, but on the offensive they will get to throw a shot first anyway. Similarly Night Stalker is situationally powerful, they can assassinate a lot of things with Cloak of Fear and Black Prayer, but all it takes is a True Sight and/or some good high resist units to make them impotent.
Ultimately, what makes Death hard to play is that their summons are generally specialized, they can't buff their regular units well enough to cover the gaps, and even their spells do not fill them. Death also has a major power gap between Shadow Demons and Death Knights/Demon Lords - Vampires and Wraiths are too vulnerable to really work as the cornerstone of Death armies in Rare tier. This means that Death infact needs heroes even more than Life or Sorcery - the realms intended to buff heroes. This is quite counterintuitive, considering that Death has little to offer a hero outside of Wraith Form for stopping Web/Crack's Call, and Vampiric to heal themselves and raise undead. Egoism is okay for atleast getting heroes levels faster, and Stealth is nifty for scouting lairs. Dark Force seems way too risky to rely on, especially since heroes generally don't get much HP until they reach high levels, and enemies tend to stall when they can't win.
My suggestion for Death is honestly similar to what I suggested for Chaos: make it more versatile at the Uncommon tier. It's a shame that Death is supposed to be strong in the early game, yet can easily run into roadblocks they can't deal with.