It's funny, I actually found the AI in Medieval to be just as silly... If not more so...

In medieval all you had to do was build a half-square against the battle boundary and the AI would never try to outflank you, because it couldn't send it's troops past the battle boundary. As far as I can tell, you can't deploy at the battle boundary anymore in Rome, and the AI always tries to flank me. I never seem to have quite enough infantry to form a half-square either, I'm not sure why that is, but I think it's a matter of having to deploy infantry in deeper formations in this to get results. In Medieval I could deploy a formation 2 or 3 deep and expect it to hold against heavy cavalry. Doesn't quite work in Rome.

I actually saw more parading in Medieval than I ever have in Rome...