Underestimate the AI: Reap the consequences.

[Graeme Dice]

Originally posted by Cainehill:
A human-played army would have to first go through its pre-scripted spells, regardless of the fact that many of them would be near-useless (certainly by comparison with Banishment), before finally settling down to kick some undead butt.

You could achieve exactly the same thing by placing all your commanders on "stay behind troops" or "cast spells".