Well said, 4decadepro.
It's true that, except for the strike years, amateurs have had difficulty breaking into the pro ranks. Certainly, there were organizational and cultural obstacles. Many Americans were able to do it though, and, looking at that list of greats you provided, I don't see how they could have been stopped.
You can still feel the tension and resentment in the amateur ranks. Maybe, they have some justification, but there's a level of dislike and backbiting that goes beyond competitiveness.
Hopefully, the jai-alai winds will change again to open up enough new jobs that we can put this behind us.