KE deals some heavy damage when specced properly. Blade allows for very low cooldowns (maybe not as good as an artificier in a high crit party, but you're only constrained by mana anyway) plus KE has one of the best damage/mana abilities. 1000% damage for 20 mana while also making you invulnerable? Yes please. WB on necro deals 2000% + 600% explosion but it's a DoT and costs 65 mana, so Fade Cloak is still more efficient. Rift might have a higher damage potential because of unlimited mana, but I'm not sure. Melee chars also lose out on some dps due to the need to reposition so it's another consideration.
KE damage potential is probably not as good as rogue specs but it still can mow down pretty much everything very fast while being in zero danger.
In terms of auto attack, 2h reaver has the highest auto with proper gear, but it does not matter much since most OP builds can spam some abilities 24/7. In terms of best sustained damage it's artificier most likely (but it's a very late bloomer, so I have to say KE for the most part of the game).