I'd be more concerned about your dps if that was your output with a good offhand and higher expertise.
Honestly I think a lot of the "missing" dps is low expertise + crummy offhand. Just fixing those two issues should have a very noticeable effect. Farm up another edge of ruin and use expertise food until you get gear/trinkets with expertise on them in the meantime, would be my suggestion.
EDIT sorry if this is something you already know, but also make sure you are DPSing from behind the mobs.