Perhaps manorialism rather than feudalism, which implies certain bidirectional duties.

It may not be a huge improvement when identities and posts can't be migrated, but it's still an incremental one.

While I don't really know about posts being migrated, identities at least can be migrated in the common circumstance of someone simply wanting to change providers and the old host being willing to hold onto the "moved" record for long enough

I don't think that is correct? You can spin up your own instance and do stuff on it. The fact that some people want to share their resources isn't feudalism.