I don't think his conclusion is necessarily accurate, but his premise certainly is. In France, they play large centerbacks, and usually run a destroyer CDM so it is difficult to have a large degree of build-up. NOTE: I have very little experience with Ligue 1, but based on what I've seen and the players who start it seems logical.
On the other hand, he's 100% right about La Liga. A 5'7 winger is pretty much the norm for nearly every position in La Liga save GK and CB. Try that in France against the man mountains in defense and you'd be killed on a weekly basis.
Spain in general, the national team, and La Liga adopt quick, even cute, passing combinations that are adept at moving around defenses that are - by definition - movable. In Ligue 1, they are far less movable, and therefore less vulnerable to the type of soccer that is played in Spain.
My conclusion from that would be that Spanish giants would win just as easily, but by far fewer goals. A 2-0 win isn't that different from a 7-0 win in terms of effectiveness or doubt of result, just perception.
Paris Saint-Germain midfielder Marco Verratti says he doubts Spanish giants Real Madrid and Barcelona would win Ligue 1 matches as easily as they do in La Liga.
Is he even serious?