You're making selective arguments yourself. Yes, we won the WC in 1966 - with home advantage, something that really mattered then (we'll gloss over 1962) - but the England team wasn't just about the top clubs. The 11 players who won the cup came from eight different clubs. If only players from...
Easy is totally on the ball here: there are 20 squads of 25 - 500 players - in the PL. If 30% are English, that's 150 top players. How many does Southgate need?