This kind of comment is a disservice to all the engineers who actually figured it out. Elon Musk is certainly a visionary and a financier, but is not a 1000x engineer/mathematician who did all the work himself
Go listen to Tom Mueller on the design choices made for the Merlin example.
But of course nobody does everything himself, but for some reason I read this sort of comment made about Musk in every single thread but not with most other people.
Bear in mind that the first time one of his staff proposed verticals landing rocket stages, he laughed.
Go listen to Tom Mueller for example. Musk himself says at SpaceX 80% of the time he is working on engineering not traditional 'CEO' things..