It does block them more so than on fedi. When I block someone they can’t see my content nor account, they can’t log out and go see my content. It’s not just filtered, also they have banned accounts and removed content

Those aren’t the kind of forks that this article is addressing

No, I’m talking about making extensions to the protocol that becomes the defacto standard

They don’t have to take energy to adopt the format. You do realise that current ActivityPub services don’t support all services and features of the other platforms? You realise a great deal of Fediverse utilises Mastodon’s implementation of AP? So a lot of what people are worried about Threads doing has already been done by Mastodon.