When I attack settlements all leaders armies behave the same every battle. If the settlement has no walls they come running out, and if I deploy my entire force all tight together the enemy comes out all blobbed up and tight together to eat all my trebuchets and archer spam.
Have to admit I really enjoyed it the first playthrough watching everyone burn, but it is so predictable that it kills the replay value of battles like that.
What I would like to see is a system where the ai's Army behaves differently based on who is commanding it.
Zhuge liangs force would be smart enough to stay inside that settlement and make you come to those choke points, even if it doesn't have walls. If he is eating treb fire spread formation everyone and also put distance between themselves and other units. Run them fast back and forth stopping a lot to mess with the trebs fire etc. He was a genius, it should be annoying to fight his army instead of being (in battlefield actions) just the same as any other random general.
Then there would be gens like Zhang Fei who would yell 'charge' and head on out.
And all the other generals would be somewhere in-between and less predictable.