Look, Shaw is what he is now. He will not be better. Or worse. He is a player who will do his job in defence against most teams and in attack he will not offer much. Even against smaller teams at OT he is not doing much. True, world class full back will be in attack against those teams all the time. Look at Alba, Marcelo, Carvajal, Juve's both full backs... they are there. All the time. Crossing, beating their man and overlapping.
Shaw does that one or two times per game. His crossing is average at best and he can't beat his man. He is just defensive full back. Excellent defensive full back. But is that enough for Man Utd?