I've seen the AI work both ways in MTW. If the AI thought it had the advantage, it would rush a full battle line at me, forcing me to withdraw my archers. In fact, I learned on map's edge to take them out of skirmish so that I could pull them back behind the line (because they would often end up routing away-with skirmish on expert-or turning sideways.)

On the other hand, I've seen the AI do piecemeal attacks in MTW that wasted good units to archer fire. Sometimes it would stack its units foolishly, but mostly on defense.

On average, the AI was more likely to do a full line attack in MTW than RTW from what I've seen.