You don't know what you are talking about.
All EuroLeague teams are the same teams that compete in their national club league. They just qualify to also compete in the EuroLeague.
Same thing nationally. Spain and Italy have a Series A league, B, C, etc. It's almost the same as our baseball system, except technically they are all interchangeable teams. The worst teams are 'relegated' to second tier status for ensuing seasons while the best teams of the second division can be promoted.
And these aren't pro teams in the same way we think of them. They are community clubs that have their own developmental youth teams and often cross a variety of sports. For example, if FC Barcelona sounds familiar, it's because it's the same club that has he soccer team (FC stands for football club).
I think it would be accurate to say that the Series A league of most top countries (Italy, Spain, Greece) would be slightly better than high-level college. If you get to a country's third tier or so, it might be comparable to D-2 or maybe low-level D-1.
You take the best from these countries and put them in the EuroLeague and the competition is better, though still not comparable as a system to ours. There are players who are not in the EuroLeague who are better than players in the EuroLeague. The EuroLeague is not designed to monopolize all the top talent the way, say, the NBA is.
One other thing. Players do struggle to adjust here, but more to style of play than anything. Over there they pass, cut and shoot more. Here, it's more about the dribble, on-ball screens and penetration.
A lot of good Amercan players who you think would do well in Europe struggle there for the same reason.
Funny, Brandon Jennings sucked in his one year out of HS plaing in Europe. The next year, he was one of the top NBA rookies. And Ricky Rubio was better last year for the T-wolves than he was in Badelona, where he was generally considered a disappointment. But he has an American-style game.
This post was edited on 3/3 at 1:31 am