Ignoring the DPS entirely (which is not a small issue) DRG's other problem is that they are literally impossible to bring into i110 Final Coil progression and survive, due to their lower magic damage. Especially if you're giving up a MNK's DK to bring them.

If you were to rate DEF/MDEF on equipment from a scale of 1 to 4:
Tanks are 4/4
Mages are 1/3
DRG is 3/1
Everyone else is 2/2

DRG equipment needs to be buffed to 3/2 to be able to survive extreme amounts of AoE, or evened out to 2/2.