You just listed a whole team of players better than Maguire who've either done far more for Man Utd or are still learning the game, or in Rashford's case both.
The idea that Maguire is getting more abuse than the likes of Fletcher, O'Shea, Phil Neville (from England fans), even poor old Phil Jones is laughable. The difference between them and him is some humility and desire to keep working and improving. I'm not saying Maguire doesn't have that, he just hasn't shown it or even really said it. Phil Jones didn't go round blaming other people for his mistakes or injuries, even to this day he just does his best to get on with it and takes the flak because he's a decent, responsible guy as far as you can tell. That game when Jones returned after 2+ years showed more character than Maguire has in his entire career unfortunately.
The idea that there are Maguire fanboys out there is quite funny though tbf, he's hardly an exciting player even at his best