I did not read the link, but two of my biggest concerns do not appear in the summary you provided :
the burden of hosting an ActivityPub enabled service is often duplicated for each instance instead of being split between them (for example, my Lemmy instance has a large picture folder and database because it is replicating all posts from communities I’m subscribed to)
it’s a privacy nightmare. All instance admins now have as much spying power as the single centralized service it is replacing
I did not read the link, but two of my biggest concerns do not appear in the summary you provided :
(Edit: typo)