This is a silly argument. That wealth is already there. If the people with privately held wealth wanted to support research at the level that it is at now, then they could already do so. The fact that they do not does not lead me to think they would once USA funding gets terminated.

As I understand it, you are arguing that if the system was inherently good, then others would try to replicate it. I would then counter with if we had a good system, why should it be destroyed?

We have been able to reach enormous heights thanks to government funding, and no other system could have replicated that success. In every scenario where government funding is eliminated, the level of research progress goes down. As long as you understand that, then you can stand by your statements, but do not fool yourself into thinking we will continue making as much research progress as we have been for the last several decades.