The simple fact that I don't think you can argue now is that he's just not as good an all round player as we hoped he would be. The whole 'on his day' argument is pointless when you have a mature player because it's not like you will see their attitude change from the usual rash form of a promising teenager or player in their early twenties. Pogba should be at/near his peak at 27. I don't even think it's a matter of concentration, as always comes up in these conversations, but rather a question of footballing ability overall. I don't think he's close to being world class but he's still a very good player and, maybe somewhat counterintuitively, I still think he can be successful here.
Once we accept his limitations and learn to accommodate him & not expect him to dictate a game, we should be much stronger as a team. I think the solution is easy; he should never start as a lone DM or as part of a 2 where his primary role is defensive, he isn't good enough for the players we have to support him in that role (versus playing with Kante for France in front of an elite defensive 5 and with world class attackers ahead of him + Giroud as an out ball), his role with United HAS to be a creative, attacking one otherwise we're wasting our time and his. He has looked his best when linking up with Ibra and then Martial, when he understands an attacking player he forms a good link with them and he needs to be receiving the ball in vastly more advanced positions than he currently is - which for me means we should be transitioning to a more possession based, positional game and not the direct, front foot football Ole wants to play because we have bought the wrong players (AWB doesn't suit that style, Maguire is terrible for that style, James is not good enough, Bruno probably does in fairness) and everything points to a fundamental issue between our tactics and personnel. Until this changes we'll do ok given we have a really good team with some depth but I can't see us doing any better than scraping 4th with the more likely scenario being a return to the Europa.