Going from Normal AI to Impossible AI...

[Edi]

The AI will buy staggering amounts of good quality stuff if the low quality chaff is unavailable. Try the Better Independents mod, which disables the crap infantry types by skyrocketing their gold costs. It leaves archers available and in addition to those, you'll start seeing a lot more nationals among the AI armies.

Nothing like seeing a scouting report that reads that there is an army of 750 units in the neighboring province, consisting mostly of Principes, Hastati, Equites of the Sacred Shroud and Archers and when the 400 Principes 70 Hastati and everything else actually begin to roll over you...

EA Ulm is similarly brutal with that mod, it will bury you if it gets to expand early on. The AI will also build a lot of castles, labs, temples and other stuff with the extra gold.

BI is not compatible with the full CBM, but you cna use parts of CBM such as the gods with that, since BI only modifies units that appear in independent poptypes.