Southgate has a system that he plays and it's proving to be very successful as his record shows. Pep has a system, Klopp has a system, Arteta has a system etc etc.
What they do is buy players from other club who will be able to play in that system. Pep won't buy, for example, Jamie Vardy as he's a player who works in the counter and he simply wouldn't fit into our team no matter how good his form is. We wouldn't buy a tough-tackling midfielder as it wouldn't suit our style.
What Southgate has done, and few other managers have done, is copy a winning system from another English club manager. Maybe Venables and Hoddle had the nouse to do it. Southgate has copied Pep and the idea that the best form of defence is to keep the ball, the way to win a game is to keep the ball and the way to dictate the play is to keep the ball. As a result, he picks players who are good with the ball. It's no good being a top class defender at Crystal Palace if you can't pass it - you won't get Pep after you and you won't get Southgate calling you up either.
Anyway, this is why he picks Maguire, Phillips and Henderson - he trusts them and he knows that they can play his system. If we decided to pick players on form, the team is constantly changing.
It's all very well saying "we need a Bernardo or Gundogan", but they are exceptional players and at the national level, you can't buy them. So you have to pick a system to suit the players at your disposal. He's done it very, very well so far and brought a lot of harmony to the England set up.