I don't want to diminish the greatness of this champion, but frankly i wouldn't count the results achieved in USA. He's a giant among children. Just to make a comparison... Mozart is Mozart. You don't add anything to his greatness if you put Mozart agains a classroom of first grade music students.
The MLS is definitely below European standards. That said, he has scored some wonderful goals... goals that he would have scored even if he was in Europe. As a North American, it's nice to have Messi in the MLS. I've been enjoying the spectacle. I've been enjoying having games played in my time zone. Not to mention that it's sort of a Cinderella story in that he arrived to join MLS' last place team, and pushed them to victory. As for counting the trophies, the "Penaldo" fans are going to be counting his Saudi trophies, so we shall do the same.
Maybe it will help grow the league. Move us up (at least a little) on the world stage. At the very least it will be a good lead in for the next world cup held in USA/Canada/Mexico.