In short, no matter how strong humans are, their ultimate ability isn't really that super, and it needs to be balanced somehow.
Regarding the Dark Elves – they worship the Dark Dragon, not Chaos. It's logical that they would primarily benefit from Darkness for their ultimate ability, but since they specialize in Chaos, Chaos shouldn't be completely excluded. Therefore, I think the path to their ultimate ability should be through Darkness, Chaos, and Sorcery.
Блистает там воздушностью прогалин.
Но между кедров, полных тишиной,
Расщелина по склону ниспадала.
О, никогда под бледною луной
Так пышен не был тот уют лесной...