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:
So long as people who care about where their instance is hosted and don't like the big hosting providers can easily find services hosted elsewhere, I don't think it matters too much. But perhaps you can go ahead and start working on plans to some day decentralize web hosting in general and I'm sure lots of people will join in once the worst of the problems at the application layer are solved.