You see, this is the thing. It's very easy to say what you are saying, that if Southgate has that position and is so well considered there must be something that he's doing right and that I can't understand.
But if you think about it, that's essentially wishful thinking, or "surely the people who hired him can't be that stupid/ignorant"... but sometimes, that's exactly what happens. People hire other people with the hope that they'll be good. Some people posted the documentary on Salford City, who were playing below the Football League, and I promise you I could set up better coaching sessions than the ones that coach set up. Would I be able to handle a locker room of 20 players? That's a different question; but the training session was poor.
And of course, I'm far from saying that I'm an expert. Even if I had a Pro license I wouldn't claim that I know it all, but once you get into the habit of watching training sessions you sort of train your eye, and in fact there have been times when I've said "this doesn't look entirely right, but there must be something to it". When that happens, I read and research to find out what I missed. For Southgate's session, unfortunately there was nothing to learn really - except from learning what not to do in my sessions.
And there's also the factor of "schools" or "philosophies" of football that make one person go "this session is great" and another person go "this is rubbish".
I've attended a few training sessions of U-6 which are led by a coach with 20+ years of experience, and he allocates 5-10 minutes to teaching the kids the Cruyff turn, step-overs and a couple of tricks. He says that the sooner these kids learn these tricks, the better they will perform them when they're older. I, on the other hand, have decided -so far- to follow the lead of Michels and think that at these age (U-6) the sessions should be aimed to the enjoyment of the kids, so that they develop a bit of love for the game. Make them run with the ball, laugh, maybe play a few games of tag, and finish up with a couple of brief 3v3 matches. Let them enjoy themselves. And believe me, whenever these "technical sections" of the session begin, a few kids just stand still looking fed-up because they can't pull of any of those tricks, and they feel so frustrated that they don't even try. This, in turn, means that they'll be frustrated for the rest of the session because they know that they are worse than other kids who at that age can dribble and do quick turns, step-overs, etc. In this specific case, I know this session has a failure although I have less than 1% of the experience this coach has.
I think your tip is more appropriate for people who think they know better than anyone else, and that all coaches in London, England, Europe, or the world are stupid or don't know shit. I'm not saying that at all. I'm just saying that I expected MUCH, MUCH better from the head coach of a national team's U-21. It's a key moment for their development and you need someone who would guide them correctly, and it didn't look to me that Southgate has what it takes in terms of "session portfolio".