Based on the two previous games I played, I wasn't completely convinced that 2UPT did not help the AI. (Mainly because I had neighbors who seemed uninterested in going to war, so I ended up having to DoW them to get things going.)
So, I tried one more time. Played as Babylon on a tiny pangaea map. Selected Greece, Aztecs, and Mongolia as my neighbors. (Rather a fun setup. You know they are coming for you sooner or later.) Got attacked repeatedly by all of them, and saw absolutely no indication that 2UPT changed anything for the AI. Monty made the usual jaguar rush and came through the bowman gauntlet in single-file. Alex put together two different mixed troop attacks (first with hoplites and archers, second with pikemen, archers, and companion cavalry). Both attacks came across a broad front, with no stacking. Genghis made his attack before getting keshiks, and did nothing special. As part of a later war, he had the usual difficulty in taking the city-state of Venice. Went after it with four keshiks, two trebuchets, and one pikeman. Lost the pikeman because he kept attacking with it before wearing down the city defenses, and took six turns to get another in place to actually capture the city. I fought purely defensive wars up until I could raise trebuchets and longswords, and ended up with a domination victory. The AI has even less of a chance defending against a human attack that exploits 2UPT than he does when using 1UPT.
Now I'm convinced. Of course, combining 2UPT with some of the other tweaks that nokmirt suggested may still improve things....