[Uh-Nu-Buh]

Equip your priests with boots of quickness. Use 2-4 priests lvl 2-3 per army. Script your priests to use banishment over and over. 50 HI plus 4 such priests can kill 400 undead army very quickly. You need standard bearers/priests too, to keep morale up.

Use inexpensive archers--they can't hurt your heavily armored people, but they eat up hordes of undead. Throw a small wall of heavily armored high morale spearmen/pikemen in front of the archers.

Overland spells of fire can decimate undead ranks.

Ermor has powerful living infantry, and great mages. A person behind Ermor is a horrifying thing, an AI on the other hand is not so bad if you take the obvious steps.