If the USA didn't accept the Europeans, Pinoys and Asians, The American players would have done better financially. The level of play would not be as high though.
If the USA had been isolationist and not allowed players from other nations to come over and compete and add to the pool scene and instead the international pool scene was fully elsewhere and not within the USA at all the game would be 100% completely dead in the USA by now.
Guys like Mika, Appleton, Dennis, and others that come over to the USA to compete are what help to keep pool in the USA alive. Without them who the heck do you think was going to keep the game going other then SVB and how would even he get the world class training he needs to compete on the global stage? His game has improved hugely because the USA has been fortunate to have some world class foreign players decide to call it home.