I think Emery likes him, likes his work rate and his over contribution. He's started popping up for goals and also creates chances. His biggest problem is misplaced passes, not the attempted defence splitters, but the simple ten yard ones. It must be a concentration thing.
Currently Buendia (and McGinn) are our best options in the advanced midfielder roles. Until we sign better, or JJ and Coutinho step up, then they will be starting.