I agree with Parmenio. Something was lost in the MTW to RTW transition. MTW AI armies were very good at forming up battle lines outside of arrow range, then charging them en-masse into your battle line. In RTW, I rarely see that. It's like they get close, then they individually choose targets, which screws up their formation.

There is likely a core simulation change that accounts for a lot of this (like the lead computing nature of unit vs unit intercepts). It could be the differences in Morale and Killing speed (when the AI does mass attack me, half the line reaches me first, and routs before the second half has arrived, due to losing many of their number in the interval)

It could be my experience (this is my third total war game) allowing me to "play" the AI like a fiddle. While my ego would prefer that to be true, I suspect more is going on.