I don't think of Show HN as quite the same. Nor Ask HN. I know that otherwise there is plenty of "advertising" within posts/comments/etc.

Where I think the argument that it's not social falls down is aligned with some of your comments. The feeds, upvotes, downvotes, etc. Let's not forget the spam.

Those mechanisms are pervasive across many social platforms, so why are they so different here? Don't think they are.