Jack suffers from a complete lack of position in his game. He doesn't work hard enough to be a fit for most positions, the only one that might come close is behind the striker but even then you have to get back and help the midfield. He can do ok on the left because he cuts in on his right but again he slows the game right down when he gets the ball there and obviously gives almost zero cover for the left back. He doesn't have to track back all the way to the left back position, just watch runs really, and he doesn't. He's a skillful player but without pace you'd have to swap it for energy to apply the skill, which he doesn't do.