If you gave his workers a choice between splitting the company equally with Elon and letting him have all or most of it, they would all choose to have the benefits of ownership. You can't say that someone "agreed" to something if they took the only available path.
That's post facto. What about when someone is first starting a company that could fail at any time, would workers have equally put money in and taken the risk of ownership too? People only want the rewards once they see how rich someone's company was but not when they might have to potentially lose their money if they had to invest their time and money in the beginning.
Pretty much every billionaire in existence has, at some point, taken millions of investment dollars from someone else. This is ultimately where the vast majority of their business value comes from. Compare to value generated by individuals (like book authors) which can sometimes generate millions of dollars.
That kind of individual value is more inline with the value that an individual with good judgment might be bringing on their own as an owner of an early startup who is willing to take some risks.
Basically, the risk itself isn't worth anything; paired with good judgment, the risk and the good judgment are both worth something. Really, that worth has to do with how common that good judgment is. But, most billionaires are idiots (at least at being billionaires) and their judgment tends to benefit them and nobody else. So, from a role perspective they bring negative value to a company in addition to stealing everyone's productive efforts.
You can look at how companies perform when a billionaire owner hands it off to a non-billionaire CEO. There's no sudden 20,000x value multiplier that's lost. Their role in that situation is essentially to just be privileged idiots and it's a process that's fully automatic after a certain point.
