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1. The main parameter is magic; it's easy to acquire Chaos magic through skills like Arcane Wave and elemental chains. I tend to think that yes, they are the strongest. The only problem is that mana and a faction with a large number of units can compete in terms of the "reliability" of their Chaos magic, even if not in terms of power. This applies, for example, to mages with someone like Nazir.
2. I don't think so, but they are quite good, yes.
3. We have a user on our forum who really likes playing single-player scenarios as the Dark Elves. And yes, it seems that he does it that way.
4. I take archers. Anyway, Dark Elves are weak at ranged attacks, so there's no point in trying to maintain that direction; it's better to switch to what works well.
5. Because dark elf females are damn narcissists.