I feel like these explanations based on cognitive development...they're always (unconvincingly) used to rationalize why language A is better than language B.

I'm not arguing that one language is _better_ than another... just that people are exposed to some programming concepts sooner than others. That gives these ideas an incumbency advantage that can be hard to overcome.

any attempt to prove something would have a high bar to pass.

Honestly, the best way to (dis)prove what I'm saying would be to put together a counterexample and get the ideas in broader use. That would get FP in the hands of more people that could really use it.