> it's clear from research that users prefer custom buttons if they provide more "features" than the defaults.

Hate to be asking for a "source", but what research? And what "features" can a radio button even have? You click it and it's selected. I suppose accessibility can be considered "features", but I'm strongly suspecting that the overcomplex button has worse accessibility.

> all UI controls, have tremendous inherent complexity

Well, this is true in a sense, but it's not exactly a good argument for re-implementing all that complexity in JS / HTML, instead of simply using the browser's implementation that's written in a real language.