The best thing SpaceX did was poach all of TRW and Northrop-Grumman's rocket engineers after L-M/Boeing's ULA smothered any hope of their contracts being granted. Every advance they've made was started by simply copying Northrop's designs that the Space Launch Initiative was supposed to use.
Had the US not been involved in the GWOT and had NASA not fallen for the "faster (slower), better (worse), cheaper (costlier)" memes in the 1990's it's very likely that SpaceX wouldn't exist because TRW would have gotten enough contracts to build NASA's launchers, while ULA builds USAF launchers. Or more likely the other way around, as NASA doesn't care about costs per se, but the USAF is very cost averse as they have far more launches. But we don't live in the future where the TR-106 and -107 were mass produced by NorGrom Space Systems. Instead, Tom Mueller founded SpaceX, got funding from the crazy dot-com guy who made Paypal, and answered to Gwynne Shotwell, one of the finest CEOs in modern space industry today.
Elon is just the money man at the end of the day with Tom Mueller being the brains, like the Henry Ford to Charles Sorensen, and SpaceX succeeded mostly in spite of him rather than because of him.
Unfortunately, SpaceX couldn't make a very powerful engine to rival even SLS's near 40-year old reuse of the SSME, so they ended up re-inventing the notorious N1 for their Mars rocket. This would help explain how SLS has handedly beaten Starship to orbit (and the Moon) despite Starship being in development for 5 years longer than SLS.
I think without Tom Mueller the rate of advancement of SpaceX's engine design will drop precipitously, as he is one of the finest rocket engineers alive today. Which is a shame, because they developed some pretty cheap rockets by showing vertical integration is important in rocketry. I'm not sure if that makes them as bulletproof as ULA's approach, as political integration matters more at the end of the day for NASA, although vertical integration certainly makes the USAF happy.
