BI did show greater willingness by the AI to assault, and it usually built a combination of Ram, Ladders and Tower to do it... Of everthing the Ladders are the scariest as they are indestructable and when there are 3 or 4 full stacks of a horde out there your only chance to keeping them outside the walls or they will do you will sheer weight of numbers...

I think the dismountable cavalry will make a bif difference in M2TW too, as you could often see off a an attacking Hunnic horde if you could decimate their merge infantry. But if all those HAs and generals out there could start the battle dismounted then there would be much more to worry about...