Even if SpaceX was his only company, he still is just one person. I'm not talking about Musk specifically, but CEOs generally. In almost no circumstance does it make sense to assign engineering success to a CEO in the way it was done above. CEOs are responsible for hiring executives and setting and enforcing vision and values. That's important but it isn't the whole story.
What I understand is that Musk is very skilled at taking highly technical decisions, that have huge risks and financial implications.
Take the example of the decision to re use rocket engines. Its a highly technical decision that has huge financial repurcussions and essentially the whole basis for the low cost business model of SpaceX.
