He is heavily back by research though. IQ can predict almost everything. IQ is how smart you are. High IQ individuals are mostly very curious, restless (ADHD like), so I do not think most of them are attracted to jobs where you need little IQ, i.e. bouncers.
Keep in mind that you need both high IQ and grit to succeed. JP is also a researcher, and you need to be highly intelligent to succeed in such a competitive environment. He also believes that the high IQ of jews can explain their strong dominance in intellectual fields and economy​, which I find plausible.