Shearer is a bitter cnut and I don't care what he has to say about us.
That said, Maguire does not suit the system Ralf wants us to play. Maguire is a decent player. I don't think he's an elite level player, and I don't think he gets anywhere near the top 6 sides' starting lineups. When Ole had us sit and play on the counter, it suited Maguire because everyone sat around him and he was only asked to accelerate in attack. Now that Ralf wants everyone to play a more complete style of football, Maguire is exposed because it is not his natural game. He is not a nimble and agile player. He is the kind who will put his head through a wall, but he's neither fleet of foot nor mind.
So it's not that Maguire is suddenly shit, it's that the system is changing out from under him and he's not the right player for where we are going. He's had his ups, his downs, some good games for us, and some calamities. He's not the worst player to have signed for United, he's not some stain on the badge, he's just an average player who rarely gets injured but doesn't fit into our new system.