Yes his area control and domination has always lacked something but it was never a huge problem until the last two seasons, his shop stopping and agility made up for the lack however (he was an outfield Fusbol player until he was 14 which explains his preference for punching and ability at stopping with his feet), now he is starting to age and the slowing of his relexes along with the comedy (at times) defenders the cracks are showing more. Yes a more mobile and louder defender to play alongside Maguire would help but it will only help so much. Coaching won't help now either as his style of play is ingrained. He is still a very good keeper to be fair but even the best players can't keep going forever. The time is coming to replace him whether it will be at the end of the current season or next is up to the player and management to decide.One of the biggest faults Manchester United made with DDG is long back when he first signed. He needed a goalkeeper ahead of him for at least half a season, a role model like VdS so they could work on DDGs weakness, controlling goalkeeper area.
Its clear that the current set of defenders are unable to do that, help the goalkeeper. You either bring a proper leader at the back, which is not happening because Maguire (and thats not his fault) or you fix it by changing a goalkeeper to suit 'English' football more. Someone physical to deal with the crosses since Man United players cant.
Or bring a new defensive anf GK coach and work from there.