I would argue that he's wrong. My points:
1) Both teams would be forced into the EPL shared tv revenue deal, reducing their big warchests.
2) Many of the types of diving found in LaLiga (or as LaLiga fans would call it, "art") would not pass muster in the current EPL officiating environment. Particularly because of the reputation for diving, both teams would be under careful scrutiny.
3) The EPL from top to bottom is filled with physical teams. Having Barcelona and RM deal with an upshot in injuries would be an interesting challenge to observe. They'd also experience and increase in fatigue.
In my opinion both teams would be heavy title challengers, favorites even. But I seriously doubt that they would dominate the EPL the same way they do in LaLiga with massive unassailable leads, as Raul claims. I'll also note that Raul has never spent a season in the EPL so he's more or less talking out of his arse. But there you have it.