As always I feel the first thing that needs to be nailed down is the desired job identity. And I don't mean the visual identity, "Broody with a giant sword and goopey particle effects", but the overall class fantasy that it is supposed to evoke from a mechanical perspective.

For example, we all know Warriors are the tanks that heal themselves and others. What are Dark Knights? Or rather, what should dark knights be?

Like I said before, I'd retool things as I don't like the current fantasy of Warriors, but if I had my way it'd be:

* Paladins: Support Tank
* Warrior: Absorb/Ignore Tank
* Gunbreaker: Ranged Tank
* Dark Knight: DoT/Drain Tank

So I'd give the constant (it's not bursty like it is for Warriors right now) self-healing to Dark Knights if I had to retool the fantasies behind the job, a result of moving the job to be strongly about DoTs and draining aether from their targets. But that's just my personal take, and it's also so wildly different from what they are right now that it's entirely unrealistic, Warriors would be the drain tank if anything, since they already mostly fit that.

Anyhow, I feel that without SQEX first formalizing what each tank is supposed to be, discussing what they are to do (as in, their abilities and gameplay) is a bit pointless.