Most use cases of ActivityPub would be better off as Atom or RSS feeds
Forget RSS/atom, use microformats2 h-feed.<p><a href="https://indieweb.org/sidefile-antipattern" rel="nofollow">https://indieweb.org/sidefile-antipattern</a><p>And there is existing tech for the popular reply-like-repost UX for this, based on webmention.