Put simply, the sorting / ranking is based on the score and the time published, so as long as things are getting federated within a few seconds, then federated posts / comments are no different from local ones. Mastodon only sorts things by newest AFAIK.
That implies the All feed is unique to each server, and therefore all of the sorts are also unique. Which would mean for at least a certain percentage of posts, they might be in your hot or active feeds, even though no one is really interacting with them much any more.
Should only be an issue if your server blocks other ones.