Style of play and skill level has a lot to do with it. Betis beat Madrid last year, and even though Madrid was struggling last season at that point, and dominating the game - Betis played.
Same with Barca in 2016-17 against Malaga and some other games.
Don't get me wrong, I love the EPL, I love it's culture and tradition, but the football being played between West Ham and WBA (for example) is just not on par with the football being played between a team like Betis and Espanyol.
And I'm a Hammers fan lol...
As far the quality itself... I've seen nothing that would lead me to the conclusion that mid-table clubs in the Premier League are better than mid-table clubs in La Liga.
Either way, the statement that the "schedule and quality of competition is 10x harder than any other league" is a bit too much, I'm sure you'd agree (?).
Or not.
Speaking of which, West Ham has had an oddly good transfter window and have now apparently put in a bid for Vida as well.
I'm hugely excited to see where and how exactly it will go wrong this season.