This is incorrect. The EPL is the richest league by far, and is oft-criticized for over-paying players. Pogba left MU because Fergie didn't rate him, he came back for the money.
As far as the best players going to Barca or Madrid, there's some truth in this. Especially Latino players. They can compete with the spending power in England, and appeal from a language/lifestyle perspective for South American players. It's pretty simple, the best Germans tend to go to Munich, the best Spaniards stay in Spain.
The lack of English success in the Champions League is a tough one. Some blame the lack of winter break in England i.e. fatigue, others think the style of play is dated. The influx of foreign managers (Pep, Klopp etc) has kind of muted the latter excuse.
To your last point, if Belgium wins vs France, literally their entire team plays in the EPL. Obviously England...