I know this is old, but, for mythic+ there is really only 1 choice IMO as a boxing group.

Beast Mastery hunters for DPS.

They have arguably the best sustain aoe in the game, respectable single target. WW monk might be better AOE overall, but its much more difficult to execute and is susceptible to movement. BM hunters are faceroll easy to leverage DPS out of, and they do HUGE cleave. In addition you can carry a bloodlust and a battlerez.