And how far along would Elon Musk and SpaceX be without the decades of research, development, testing, and real-world experimentation done previously by NASA and other government R&D efforts?

Your argument presupposes SpaceX hasn't benefited from the previous work done before. Which they have, immensely. Stop reducing complex systems into simple certainties. It's insulting to the entire community of scientists that have been dedicated to rocket and space research over the past 70 years.