I don't know about that. I sure fought alot of stacks. The only too-easy problems with the AI stack is that I can attack and trap them while they are sleeping in their city. That means I'm now at an advantage and they have to sally forth.

Or sometimes, I can easily lure them to attack me in bridges which mean their army getting "crushed" as the narrator would say.

Also, if the AI had limited provinces, they can't possibly build as fast. Right now, the Brutii have about 12-15 full stacks and they are at war with Dacia and Thrace (so am I).

It's the only reason why I haven't attacked Rome yet (with the Scipii about 6-7 stacks).

I only have 1 and a half stack (reinforcement) fighting in the East. Another half stack I''m building up in Alesia since I'm attacking the Britons or Germania (I'm still planning). The rest of my troops are mostly Town Watch garrison in rebellious towns as well as high valor very depleted units I don't want to disband.