df is terrible, but it really doesn't have much to do with role. If you were a healer you'd complain about tanks/dps. If you were a dps you'd complain about tanks/healers. You've just experienced it as a tank.
I've been called "literally the worst healer ever" because a tank (who had full law vit jewelry, but nq questing whites on the left side... so no mdef/def) died after taking 4 vulnerability stacks in Fractal. I've been told I have shitty aggro management because I pulled hate as blm even with quelling strikes on standard rotations.