This really only applies to the first few employees, or maybe the first few hundred if you happen to be at the next Google (so the company has to 1,000x).
After that, it's very unlikely you'd come out ahead even if the company 20x'ed compared to joining FAANG. And the other thing to consider is that FAANG stocks aren't stationary. I know people whose relatively modest AMZN stock offerings have made them millionaires.
The fact of the matter is you don't join a startup to get rich (unless you're an idiot). You join a startup because of the many other benefits it provides - having a bigger impact, working on a smaller team, less bureaucracy, etc.