He was good at real madrid but it's not when he was on the MU. You must also see the the atmosphere of the club has been giving a huge impact to the performance. Majority of players in real madrid at that time when ronaldo was there have very big capacity unlike when he was on MU.
You might see how bad meguire and he is still become the main starter for the club. So, you can't compare the atmosphere of MU with real madrid.
You're right it's a very different situation when he was at Real Madrid, but it's the same situation when he was at Manchester United in the past. It's not about comparing the performance of one player to another. But here the role of the players in their position will determine the team's performance.
Maguire, yes this one player is still very questionable his role for Manchester United, whether he really plays for Manchester United or plays for the opponent. Lol