For what it's worth, among me and my siblings, the one with the best social skills, the widest circle of friends, and who is still most in contact with childhood friends is the one who was homeschooled.

No, that wasn't me. I certainly spent a lot more time interacting with other kids my age during weekdays, but quantity isn't quality.

I'd be curious to know if there's been any long-term research on this subject, but I'm not aware of anything.