Hell if you joined Facebook last year and got in when the stock was around 100, your initial equity grant just 5x.
Decision inertia means that employees often don't sell vested stock, and end up being lucky. Similarly, external investors aren't willing to put 30-50% of their networth into one bet and therefore miss out on the kind of luck that can set them up for life.
There is nothing that a lowly engineer at Tesla or Nvidia knows, that can't be found out by an external investor. They are operating in the same information landscape, but different outcomes when they give into decision inertia.
It's not about joining Tesla or Nvidia early. It's about betting on them.
It's also possible to bet on Tesla/Nvidia and lose. Badly.
That was a bet.
If they hadn't made the bet and sold stocks as soon as they vested, then the returns wouldn't have been as incredible.
The real point is that it's misguided to try and compare percentages of tech company employees with percentages of founders; they're very different things.
Of course, out of all the founders of all the companies, a relatively tiny percentage will be vastly rich. And out of all the employees of all the tech companies, most will be quite wealthy and comfortable, and a small percentage will be vastly rich.
But that doesn't tell you anything about what is the most reliable path for any given individual to get vastly rich; it entirely depends on whether you're the kind of person you are how well you can learn how to build successful products and companies.