Doesnt /stopcasting cause your melee swing timer to reset? So if you are spamming that you are actually lowering your group dps. Im not sure this is the case anymore.

I have so much time invested into my DK I really dont want to drop him from this group, but I know my paladin tank is so much better at tanking (he doesnt die in 3 GCDs to stupid npcs in FoS).