Which magic schools should I choose for the late game? Or should I go for a specific artifact?

question: how to play a duel with Razazak against Marbas? or Oroi against Marbas.
The golems of Razazak are useless. They are destroyed by archdevils in one or two turns. There are only 9 mages, and they heal with fireballs, but not much. Razazak doesn't have fireballs at all. The golems are falling apart. Teleport to the enemy's rear? To whom? Sorry. To the succubi? 60 of them, plus hellfire. It's great. 1 three-headed dog destroys 18 gremlins with it... :(