Thing is, the old managerial adage is that, to improve your squad you sign players that are better than what you already have. He may have improved at Aberdeen and certainly needed to bulk up, get a bit braver and become more consistent.
If he hasn't, or is a little better than when he left United, is he better than Lewis, Isi, or Castellanos? Probably not.
If he hasn't, or is a little better than when he left United, is he better than Lewis, Isi, or Castellanos? Probably not.