Which hero is the best in the Tribes of the East expansion?

I don't understand why everyone loves Lethos so much. What's the point of dark magic if you can never get Berserk, Dominate, or Vampirism in the guild? He has high spell power, but low knowledge, and darkness means that low-level spells won't have any advantage over other dark spellcasters. His specialization is also questionable, as there's too much randomness involved. And because of dark magic, you can't learn Summoning or Chaos, which can ruin your build. I think there's no doubt that warlocks have a significant advantage over many in these two schools, so why not use that advantage?