And given how much faster SpaceX has been than anyone else, I can only believe this "could've, would've" in form of the slightly longer hypothetical "if only Carmack hired all the rocket scientists (and raised all the money to give them freedom to go fast) before Musk got there".

I love Carmack, but having an idea for something is infinitely easier than actually successfully executing on it, especially as incredibly successfully as SpaceX.