England's problems to me really don't seem that complicated, but it seems that the vast majority of fans and pundit don't see it as I do. I'd whittle down to a few key issues:
Left back - Taking only one, injured left footed fb is turning out to be as stupid as it looked when the squad was announced. It effects our balance to such a degree that I'd be tempted to play Saka there until Shaw is back, especially because we are stacked with Saka alternatives for RW (Foden, Palmer, Bowen).
Deep midfield - Every top team who wants to control games MUST have a player who can take the ball in tight areas on the half turn off the defence, and instinctively play short, sharp forward passes with as few touches as possible, and have good pass selection. England have only 2 players who fit this mould. Wharton and Mainoo. You have to play one of them. I'm so against those calling for a trio of Rice, Bellingham or Foden. None of them meet that criteria for me, and against a good side we would be absolutely bossed as a result.
Attacking Midfield and Kane - We need to get passed this obsession with playing all your "most talented" players. For most fans and pundits this is currently Foden, Bellingham, Palmer, and Kane. Unfortunately, all 4 of them want to occupy the same spaces. There is room for two of them max. If you play Kane, you simply have to play runners either side of him to break the back line. So that is Bowen or Saka on the left, and probably Gordon on the right. If you play Watkins instead of Kane and he holds a position on the shoulder of the last defender, you could maybe get away with playing a Foden or Palmer type on one of the wings to drift into central areas alongside the 10 without creating too much congestion. However, only on the side where an overlapping FB will provide natural width , so currently only on the right.
Barring maybe the LB issue due to baffling initial squad selection, most of this can be easily fixed with the squad he has chosen. Southgate just needs to grow a pair, and start to prioritise balance and system over names.