I agree with almost all of what you're saying. I'm not suggesting that a social experience outside of the purview of the insular groups this small subset of religious folks experience is not beneficial. What I'm suggesting is that the particular experience offered by public schools (especially in rural and semi-rural areas insular religious homeschoolers typically inhabit) is not particularly beneficial for the socialization of (otherwise) religious homeschoolers.

I don't know of any studies (or if any could be performed, really) that demonstrate the social impact of public schools on students like this, or at least easily-identified outgroup kids. I know from anecdotal experience that in the public schools I attended that they (the semi-cultish religious kids who were not/no longer homeschooled) were not treated well, never successfully integrated socially, and disappeared from my radar very quickly after graduation. With hindsight I feel very badly about that now, and wish there some way to impact the systemic cliquish nature of public schools, especially high school. Unfortunately I lack a time machine for the kids of the past, and simply don't have answers for those going forward.

Either way, my suspicion is that public schools specifically do not offer the best (or even a much better) experience for socializing students.