HN also lets you elide branches with a click, so you're not trapped in a section you're not interested in. It's so nice opening a 400 response thread, getting 10 messages into the top comment, and clicking the hide button and watching 200 messages vanish.

Yes. Pagination can be bad if the URL indexes by 1-10, 11-20 etc. But I think HN paginates using the post ID, so that the links are permanent (?) which is a better way to do it. Basically the novel idea here is to treat the browser like a REST client.

This also means you need a predictable, deterministic algorithm, like "ORDER BY DATE DESC", but Reddit does have order by popularity, so that will not be idempotent. But now being super picky as order by popularity is pretty useful. Although I think date should be the default. And order by [what cambridge analytica-likes know about me] should be off.

HackerNews threads aren't paginated, at least not for me. I just checked a post with 500 comments on it, and they all displayed in one long list.

HackerNews posts are paginated. And there isn't any interface for navigating the pages. Which is fine for HN's minimalist approach and tech-oriented audience. But it hardly seems optimal for a general audience.