Some of my most exciting battles in Total War have been fighting defensive battles. The thing with defensive battles is that you can more easily succeed against the odds, because you get to occupy the best terrain, and the attacker has to go to you, because they lose when the time limit runs out.
Bearing this in mind, why is it that the AI abandons defensive positions by retreating from battles?
It would seem to me that the AI never has a chance of gaining the skilled defender or skilled last stand virtues because the AI never chooses to fight such battles.
I imagine this isn't something that can be easily modded...