For England he is correct. Yes you always need to prove yourself as a footballer to get picked in the team, but I don't think this is what he's referring to. I think he's referring to the implication that he's not good enough for England, shouldn't be picked for the squad because of his club situation etc. Which isn't the case, he's one of the best options of a bad bunch of centre backs. It's very clear this is what he means and the criticism he's attempting to combat because he goes on to talk about minutes played for United.
The United comments are a statement of nothing really. He's played some games and can't remember losing.
Agreed. At this point, it feels that he could say "good evening" and some people would still get all riled up. The lengthy answer he gave, going into details and stating his version of the facts, made him look more defensive than arrogant.
I also think that the noise surrounding Maguire during the international breaks is down to Southgate. It's clear that he has a core group of players he trusts no matter what. He's neither the first nor the last NT manager to do that. But when they ask him about it, he doesn't really want to be held accountable for his choices. One day it's "some players are good regardless of how many minutes they get", the other you get something along the lines of "there's a lack of depth and quality in some positions on the pitch", and he never forgets to add a note of authority like "i have warned them that if they don't play with their clubs, their place in the NT can't be secure". He's the one who's sending mixed signals to the press.
As for United, i think we should revisit the policy of coughing up world-record fees and amortizing the cost to the length of the contract because "the manager said so" or because the scouting department can only come up with the obvious choices. It would do us a world of good.