Playing in the MLS certainly hasn't hurt Messi, who's playing better soccer now than he did at the end of his tenure with PSG despite being close to 40.
Also, I said that the MLS needs to continue to improve, which it has. I also said that it's my hope, repeat hope, that eventually the MLS will develop to a point in which most of the USMNT will play in it, because I think that it's always best to have most of your national team players playing in your domestic league.
Finally, obviously, the MLS isn't comparable to the Premier League, La Liga, the Bundesliga and probably even Serie A. However, IMO, it's not that far behind, if it even is behind, the other European leagues and even the English Championship.