The first time a Necromancer attacked me, in battle, he managed to cast 8 times, and 7 of those were Raise Dead.

Based on this statement, I conclude that you were playing against the AI. And, judging by the spells the opponent used, it was on Warrior difficulty. And that says it all.

I advise you not to draw conclusions about the balance of power between factions based on playing against the AI. The AI is, by definition, as dumb as a doorknob; its task is not to win, but to lose gracefully (although even that it rarely manages to do).

Believe me – playing against a human, you would have faced a Berserker or Puppet Master, a Phoenix or Fire Elemental, Vampirism and/or mass debuffs. But definitely not Raise Dead 8 times in a row.