It's true defensively, he's quite pathetic but that's not the main reason United (over)paid for the player. I would have preferred Pjanic and it would have cost United a fraction of that fee.
IMO, Pogba has two outstanding qualities for a midfielder-vision and passing(long ball). His work rate is also the highest among the midfielders. He needs to hone his attacking instincts and shoot when the opportunity presents itself. All too often,he holds the ball far too long and dribbles unnecessarily. He has to be mindful of the fact that there are no Vidals or Rossi around to assist. Defensively, he's hopeless- a disaster with man marking and tackling.
United can rest comfortably knowing that Barca and Real will not come knocking on our doors anytime soon. Pogba will do well if he can measure up to Scholes qualities.