I think the critics are fully justified at this point. I don't watch United that regularly, but I have seen some matches in which Donny featured, and he simply has been woeful. Absolutely horrible. So negative in his passing, no initiative whatsoever, no threat whatsoever, he purposely seems to make himself unavailable for the pass. I'm truely amazed by how bad he has been.
However, and I cannot stress this enough... he was a good player at Ajax. Ofcourse, the Eredivisie is on a different level than the premier league, no doubt about that. But he showed it in the Champions League as well for Ajax, quite frequently actually. Plus, Donny has been utter shit against bad cup oppositions as well for United, in slowpaced, low intensity matches. It is not just a matter of the high intensity of the Prem being too much for him. I've seen Donny for +- 4-5 years in the Ajax first team and his body language is unrecognizable. He seems extremely shot of confidence and, given the total lack of initiative and positive impact, his play shows. He seems completely out of place.
I think, barring a total mental reset come summer, there is no way back for Donny at United. It simply seems like a total mismatch. Maybe Donny is just a system player, who knew the Ajax system from his childhood days, and simply is unable to adapt. Or maybe he can adapt in another environment, with another team. But the way this is going, there is little hope for him at United. I hope he proves everybody wrong, because he is a good lad, with great work ethics (although it doesn't show at all at this moment..).