I'd suggest that social development can be served by literally just playing with friends though. In our area, the YMCA offers sports basically the whole year, which is a good way for the kids to spend time in a structured group setting (and if you're lucky, you can even be the coach!), and my wife has found plenty of fellow homeschoolers and unschoolers on FB who are looking for some social interaction for their kids (we happen to live in a place that isn't particularly religious though).
Relatedly, everyone just seems to agree that the socialization provided by school is good and necessary, and I'm not so sure that's true. It's been our experience that all of our friends and relatives, when they do complain about school, complain about bullying or kids otherwise misbehaving in a way that's stressful to the child in question.
In addition, our experience on the playground has been that kids who are in school tend to be way more likely to be rude and aggressive. And I don't say this to suggest that school makes kids rude and aggressive, just that I have 4 kids and I have spent a lot of time around a lot of different kids and I've seen zero evidence that school provides positive socialization beyond what could be had by attending regular play groups.
That is, socialization in the public school system very much has a downside.
I mostly just want to remove socialization as the deciding factor that makes parents keep their kids in school when they'd really rather do something else, because, as you say, socialization in public school very much has a downside, and I think at best, it's a wash compared to homeschool.
And if you shield kids too much such as by over structuring their life, they might be defenseless later on. It's a fine balance and requires care, care which neither schools nor homeschooling parents are likely to be able to provide. Not even specialists most likely.
It's an open question.