That's true. There are players from La Liga that did well when they switched to the EPL. But that doesn't mean that the EPL isn't tougher than La Liga. The EPL is the toughest league in Europe, especially this coming season where there are more good managers at good clubs. In La Liga, there only two clubs fighting for trophy, well now 3 with the recent emergence of Atletico. But historically, in La Liga there's only Barca and Real.
In the EPL on the other hand, big clubs like Man United or Chelsea can lose on any given match vs smaller clubs like Stoke or Southampton. The league is really unpredictable, especially now that Tottenham and Liverpool are showing signs that they want to be in that top 4 too. Also Leicester showed us that anything is possible in the EPL.
As for Falcao and Di Maria. Falcao had a bum knee, I don't know why LVG signed him on loan. That was a stupid move. As for Di Maria, he just flopped. You can say that he didn't gel well with the team, or maybe LVG just didn't use him strategically well enough. But bottom line, and using the matches he played as evidence, he obviously didn't adjust well in the EPL. I'm not saying this happens with all La Liga players, but it happens to many of them. The defense in the EPL are bigger, tougher, pacier and more physical than what they're used to in La Liga.
Premier League has many good managers every year, not only next season, so no need to be surprised for that. And yeah, Premier League is tougher than La Liga, I admit it
But they should perform well in European tournament to prove that they are the best.
Not only in Premier League, but also big teams in La Liga got lose by mediocre team, we could see how bad Real Madrid playing in the early of season and Barca's struggling in the end of season.
Actually Falcao was being on his top performance when LvG signed him, thats why Man United fans celebrated that signing and assumed that Man United would win Premier League. They became more sure when Man United succeed brought Di Maria. Unfortunately the ending was not good. Yeah maybe Premier League has good defense, but La Liga has speed and skill.