Provider-Exclusive: “There is only the app of my provider.”
Provider-Centric: “There exist other apps, but the one I’m using is the main one.”
Service-Centric: “There is no main one and I’m trying to use the one that fits my ideal the best.”
Protocol/Ecosystem-Centric: “There exist other protocols/ecosystems, but mine is the main one.”
Fediverse-Principle: “There is no main one and I’m trying to use the one that fits my idea of an open ecosystem the best.”
Current state of different web2 apps:
I don't think that this will ever really be the case. Even if ActivityPub became public standard, there would always be other protocolls and different extensions/versions of ActivityPub. And that's good, because only then can ActivityPub continue to develop, if we have an abstract idea to compare it to. And that's the Fediverse for me.