Hmm...you weren't supposed to get a tech lead with Dan Quayle you know :neenernee.
I didn't, really. It was just the right techs. When a lead of two techs is Rep Parts and Rifling, that's enough to end the game. Player-controlled riflemen have no AI counterunit. The AIs had Military Science fairly early and big stacks of grenadiers, but against a human will not get the tactical first strike to beat riflemen. And drafting riflemen is a serious weak spot in the game balance. Besides its huge raw productivity (over 7:1 food to hammer conversion), only the human player can optimally manage the unhappiness, including a Globe Theater endless draft camp. And the human can commit to Nationhood knowing the advantage can be ridden to the end of the game.
The game was not supposed to be particularly challenging, but it wasn't supposed to be such a cakewalk either. Maybe I should have done one team per continent or something.
I think it was decently challenging. I just conquered the challenge.

You created a scenario with a set of economic handicaps. That and Epic speed naturally demanded a conquering game plan. This scenario had no brakes on that. Even civics worked that way; Bureaucracy and Free Speech were indirectly nerfed via the cottage nerf, which left Nationhood.
I rather did like this fresh approach to a more difficult game. High nominal difficulty (Immortal+) entails locking the player out of the military game and pushing him into exploiting the flashpoints of the economic game (bulb and trade slingshots, Liberalism.) This game did the converse, encouraging exploitation of the military game alongside bare-minimum economy.
The military part wasn't quite as cakewalky as I made it sound, until the rifle draft. Before that, you'll recall that I had to cease fire with Gilgamesh twice and skip attacking Babylon. I also skipped over a decent struggle for naval superiority in order to invade the far continent; I even used one GG for a coastal military academy just to whip Ships of the Line. Rifle drafting is a strategy that works even on Immortal and sometimes Deity, so don't expect
any Monarch game to avoid that.
Incidentally, Babylon is not a neighbor to select if you want a difficult game. Babylon was also next to the player in Pax Americana and Farmer's Gambit and made for easy games in both cases. Hammurabi's fave civic is Bureaucracy and he will never attack at Pleased, which automatically renders him zero threat.