That was my initial thought too about this theory. In any tech company competent people are always the first ones to leave on first signs of trouble. They already have new opportunities lined up and they are just waiting for an excuse to leave and probably get a pay rise on their way out. High functioning people in general tend to have each others backs because they have more to give and it's just more fun to work being surrounded by capable people rather than use your time instructing people who never seem to get it and just leech your time.

In case I sound elitist, I don't think those competent people have any inherent trait that makes them that way, it's more to do with whether you know how to do deep work, it's something you can learn.