What skills should Necromancers take when facing Orcs on a very large map?

LordViRuS, the Necromancer only managed to cast 5 spells. Could divine retribution have helped? Even if we consider the possibility of eliminating the entire stack with a single spell (although this is unlikely), he wouldn't be able to kill the entire enemy army. And what if the retribution doesn't hit? Would many tedious hours be wasted leveling up a 31st-level hero? Although, in general, without Subjugation and/or Berserk, the Necromancer doesn't really have much of a chance. However, we were talking about 3 cities. Could you provide more details? The Orc and Necropolis gains in battle were approximately equal, but if the Necromancer had several cities, regardless of what kind, he would definitely be able to achieve a significant numerical advantage.

Regarding the Orc hero, the player correctly pointed out that the hero is level 31, but the Executioners and Cyclops don't reach the battlefield on the first turn... That's just terrible...