It's under any other normal DPS and every role for dungeons until 8 man raids you'll only be able to fill the tank role. In 2.1 they could add an alternate job for MRD that works as DPS, but until then you're better off playing a different class if you don't want to tank.

Also, in Coil you'll mainly be tanking as well. An example would be Turn 1 where an add spawns for the entrance node and when the snakes split.