Our Mnk is usually around 400, sometimes more.
Me as DRG, is usually around 360.
(we're both equally geared, around ilv100)
BRD is best geared, and is up there at our dps; his dps drops a bit due to paeon, etc.
extra DRG and BLM, are around 300-350.

So i think your problem is that you got only 4 DD? and all 4 DD are low dps.
As you can see, your dps is around 100-200pts below ours...that's HUGE difference.
Your DDs need to be at least 350. Actually 400+ with only 4 DD.