Henry Ford literally invented the moving assembly line. He's also the primary reason that we now have a 5 day, 40 hour week as the standard. Prior to him (and his successes with trialing such), the typical work week was 6 days, with 10-16 hour shifts common. Marx, by contrast, achieved nothing of value for the common man, and spent his entire life mooching off Engels' capitalistic successes, while critiquing such. It's trivial to critique systems, but quite difficult to create and build things up in a way that is sustainable and means something.

As for Musk, he completely revolutionized the space industry. In modern times no single person just invents everything around something akin to e.g. the telegraph, but I don't think that really diminishes his impact. It's just a consequence of the fact that a reusable rocket is much more complex than a telegraph machine. But he's quite infamously involved and directing essentially every single step of the process. This is quite different from the detached and profit/metric motivated focus of typical management, but in many ways it's much closer to how things were 'back in the day' rather than a novel discovery. It should go without saying that people running businesses building 'x' should be deeply knowledgeable about 'x'. "Business", as a specialization in and of itself, in modern times is the disease that's killing America.