In my experience so far banishment isn't a problem from the AI (it usually wastes about 3 turns blessing and buffing before it even gets around to trying banishment). Obviously it would be slightly more dangerous with a player scripting specifically for it, but one thing Yomi has which Ermor doesn't is the ability to switch to non-demonic troops (rendering those armies of priests pretty useless).
The main danger I've found from the AI is resistant or immune to fire units, though that's probably down to my propensity to fireworks
. That thrown fire might not be accurate, but the old saying "everything counts in large amounts" holds true here (especially when combined with the poison spit). You can back this up with bladewinds or similar and crush entire armies before they can even close.