Yes, the difference between a 30s DoT and a 30s cooldown DD attack in gameplay are essentially just:

* The former gives you extra movement/mechanics resistance (as the DoT continues to tick while you move, this is important for casters).
* The former can be re-cast early, but this produces no extra damage. But might sometimes be useful depending on the upcoming few seocnds.
* The latter can burst more, sometimes important depending on the fight.

I kinda feel there'd be room for at least 1 DoT-centric job though, 4-5 stackable DoTs of various lengths, then the filler spam attack is one that drains X seconds off the DoTs current on the target, dealing their damage instantly.