DH Multishot feels very ineffective in group

It seems to me that even though I am smashing through solo GR 75-85, whenever I group for the same GR levels my DH is utterly useless. I don’t experience this power drop difference with regular rifts.

Is there a reason or might this be a bug?

Yes, and it was explained in the identical thread you made on the US forums 40 minutes after you posted here…