HN itself is fast, but the comparison I'm making is with readers that use the HN API. See how getting each comment requires an additional API request: https://hacker-news.firebaseio.com/v0/item/22481199.json?pri...

It's more about the consistency of operating on data local to the user. For example, see this comment referencing how HN paginates threads at 250 comments for performance reasons: https://news.ycombinator.com/item?id=22231055 A local database does not have that issue.