> It feels like we have sometimes accreted an amalgam of these pithy takes based on very small, one off, studies (never replicated) that let us comfortably assemble an affirmation of our broader takes.

The patterns are there and are hard to deny. The reasoning and explanations of these types of books? Don't take them for granted, do your own research if anything is of particular interest, think for yourself, etc. The books can be of value without being 100% correct.