Breach Bomb II is very good because it's 2 power. Breach Missile is bad because it's 3 power. That difference is hugely significant. Also the breach missile can be shot down by defense drones, and it's also four seconds slower. (The miss rate is the same, for them and for everything except a beam.)
Missiles are generally bad, but mostly because the damage/power stats on each of them isn't good enough. The exception is the 1-power 2-damage Artemis that some ships start with, and that's pretty decently usable, at least as long as the ammo lasts (and you really don't want to waste scrap on buying more ammo.)
Missiles are good for the computer ships because they don't have to worry about attrition or affording ammo, and because they're not smart enough to focus a burst of projectiles to pop the shields, like we human players can do with a better loadout of bursts and beams.
Missiles are generally bad, but mostly because the damage/power stats on each of them isn't good enough. The exception is the 1-power 2-damage Artemis that some ships start with, and that's pretty decently usable, at least as long as the ammo lasts (and you really don't want to waste scrap on buying more ammo.)
Missiles are good for the computer ships because they don't have to worry about attrition or affording ammo, and because they're not smart enough to focus a burst of projectiles to pop the shields, like we human players can do with a better loadout of bursts and beams.