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.
Carmack did execute, they had a working rocket, and with time they could've solved the software issues, but they didn't have the funding to blow up dozens of prototypes.
Carmack drove that project, he wrote code, he built rocket engines himself, he ran missions.
Elon, notably, doesn't do any of that. He just had more money, or was willing to commit more money, to seeing it through. For Carmack it was more of a fun diversion (the X Prize) than a business he wanted to build.
