> my understanding is the best people leave faang when they get the itch to do something better with their time.

Your understanding is wrong. The extreme majority of people who leave FAANGs don't leave willingly, and are not the best, unless it's to go to even better companies like Jane Street and the like, but those are rare.

Turns out for most people, there's not much better to do during your 9 to 5 than solving problems for half a million a year.