HN has a lot of optimizations and limitations on the user experience.

For example, I don't see the scores of every other post on HN - and certainly don't see them updated in realtime. New comments and posts show up when I reload the page - not as I scroll. There's only one HN instance - without having 100 more instances trying to mirror the content (just one - firebase).

... and HN is an example of a single, centralized, unfederated server.