I feel really bad for Maguire. He wanted to play for United just like Antony, but the system changed out from under him. I've seen memes and insults from United fans in other United groups, and it's way out of hand and unnecessary. He might not be your cup of tea (and he certainly is not mine), but I don't wish him ill, and the insults and jokes about him should stop, at least from United fans.
Anyway, I saw today why Maguire's style is such a jarring juxtaposition with ETH's preferred defensive style: watch when Maguire is running back, keeping Jesus honest, at the moment Maguire decides he's going to challenge him, Maguire doesn't bend or swerve his run into him; he basically plants a foot and steps forward bringing his entire moment to a halt. At that moment it was simply a piece of cake to get around him, and Maguire had to foul Jesus. Maguire stepped up like he was going to do a hockey-style hip check on him, when he instead he just needed to try to separate the ball from the player.
A player like Martinez (and even Lindelof) will run alongside and try and nip in to nick the ball or slow the attacker down by keeping them off their preferred line to goal. Any defender with pace will basically defend that way, but Maguire doesn't have pace and he doesn't shift his weight easily, meaning he's slow to change from his right to his left shoulder.
To sum up, I just don't think Maguire can play in this style. He succeeds in a classic "English" style of physically blocking players and clearing crosses away with headers [edit: he would play as a stopper]. He isn't nimble enough, or agile enough, or quick enough, or good enough with his feet to play in possession-based team. I wish the player well, but I don't see him getting back into the side. That cameo against Arsenal was a précis of why he won't make it.