Posts from The essence of the tactics when playing as the Dark Elves. Auto-translated

Well, what’s wrong with darkness? Sure, it can be a challenge to find high-level spells, but low-level ones can be learned from Sorceresses. Warlocks have stats that are roughly similar to Necromancers.

Well, that's the downside – it lacks the most powerful spells. Of course, under certain conditions, they can be found, either on the spell market or in another player's city, but relying on this can be risky unless you're certain you'll find them. If there's no Subjugation and/or Berserk, then a Phoenix or Elementals (considering the Sorceress's spellcasting skills!) are clearly preferable, in my humble opinion.

Yes, Phoenix and summoning are very helpful, especially in the early game, and even more so if you play with Rogues.

But what's wrong with darkness?

There's a hero named Letos, also associated with darkness, but in my opinion, he's much cooler than Irbet.