Good coaches develop good players. Personally don't think Southgate is that bad but the rest are pretty dodgy including Roy. Hopefully more will start coming through soon.
There is no doubt it, good coaching is a the centre of having a successful football nation. As is having an identifiable style that everyone buys into. British football is all about winning at development level. Children are coached on "how to win a match", doesn't matter so much about technique or skill. Go and watch schools football or underage leagues and see what is happening. Frustrated ex players are re-living their youth by intimidating kids into winning. If a team has a larger kid who can push the others about it is all about getting the ball to him.
My grandson has been playing in goals through from under 10, every week he plays on a full size pitch with full size goals, he is not big enough to reach the cross bar let alone cover the 8 yards. He has stuck at it but I have seen loads of young lads stop playing because they get disheartened. The ball is also too heavy for them, they can't hit long passes because they can't kick the heavy ball any distance.
Following this they go into league teams battling for points.
No one ever takes the time to invest in technique or skill simply for the sake of it. Even when they reach the highest levels they now are coached by people who have a system that stops teams getting regulated. There are too many managers who have worked out a system that avoids regulation. They get a young British player and mould him into a player who can "do a job" in a rigid system. They do not develop talent they develop systems.
The Premiership is competitive, it is not very good.
A root and branch change is required, changing one element of what is wrong will not get it right.