I'm just trying to figure out where you are coming up with the basis for your opinions, because I can't find anything that would reasonably support your claim.
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It's the eyeball test. When the US played England in the 2010 World Cup, we held our own with them. It wasn't based on the skill level of our players, as much as it was based on their athleticism and attitude. Yes, you can say Jozy Altidore couldn't cut it in the Premier League, but that's down to the squad, the coach, and his ability to fit within their game plan, as much as it is about his "quality".
You see US players do well in the Premier League, maybe not boatloads of them, but enough to know that it wasn't a fluke. Geoff Cameron is a starter. Deuce was a starter. Donovan was a starter. Brian McBride and Carlos Bocanegra were major contributors to their team for several years. The best Americans are able to force their way into English sides, despite the obvious bias against our players by more "traditional" English/Scottish coaches who populate the Premier League.
You have a new group who are young players trying to break into teams in Germany. You have Yedlin going to Spurs. You have guys playing in the Mexican League, several of them, in fact, and the Mexican League is not that bad.
Then you look at International results - yes, some of them were friendlies, but the US has shown that, on its day, it can play with the best sides in the world. In the last 20 years, we've had major wins, beating England, drawing with England at the 2010 World Cup, beating Columbia, Portugal, Mexico ( in the World Cup), Algeria and Spain in competitive matches, all prior to Klinsmann becoming the coach.
Since then, we beat Germany in a friendly and gave them a pretty good game at the Brazil World Cup, we beat Italy in Italy, Ghana in the World Cup, drew with Portugal at the World Cup, beat Scotland, Mexico at the Azteca, Turkey, Nigeria, the Czech Republic, and Costa Rica. We had a streak of something like 13 competitive matches without a loss. Foreign coaches may sneer at the perceived lack of technical ability among US players, but our teams routinely out-perform expectations, if you were going by skill level alone.
That's what I'm basing my opinion on. Just because a coach in the Premier League is thinking short-term and doesn't want to take a chance on an American doesn't mean that the American couldn't do well if given the chance. Our international results bear that out, in my opinion. And it's these players (and even more talented, skilled imports from Central America and the Caribbean) who make up the typical MLS team.