The major issue with Maguire is that, even at his best, he does not suit a progressive and pressing team. He is too slow to be relied upon to deal with any counter attacks from the opposition.
This is a big problem I had with us signing him in the first place. It showed that we were never moving towards a pressing system under Solskjaer. Maguire has only ever looked his best in very defensive sides that sit back with heavy cover, and that includes Manchester United during his time here.
Both England and Manchester United have two players in defensive midfield to cover him. If he was 'that' good, would these managers need to do that? Do we really want a defender that we need to make allowances for? It is not something that will work in a high pressing system as our midfield needs to drop too deep to make up for his inadequacies.
I think Maguire is going to go down as, potentially, the worst signing Manchester United have ever made. He is not suitable for a top side with the way the game is played, nowadays.