I think that is the problem. When you go from leveling warrior or PLD(at later levels), switching to DRK can be brutal because you dont have self healing like that anymore, so you have to learn to depend on the healer and your mitigation more. This is more of a tank design and content design problem but that is why leveling DRK is probably the worst to level out of the 4 tanks. Its great at endgame but leveling its really bad.