And of course all the dynamics you talk about emerge naturally. With scale comes concentration and hierarchies out of necessity, the power to blocklist 'relays' across the largest instances, etc.
All these experiments basically are a venture in rediscovering economics and politics. The internet started out decentralized. Reinventing html and web servers isn't changing anything.
If so it’s only a happy path and doesn’t handle the very common migration scenarios of falling out of favor with your server owner.
If this happened, users would be free to opt-out of that and switch out their client and/or relay with other options that fit their needs without friction. They would keep their identity, note history, friend list, etc.
Could be as simple as one client releasing a UI change the user hates. They could just download a different app and keep going.
To be clear, Damus already offers some level of content moderation. Other clients are accepting PRs to implement as well. Nostr itself offers some level of centralized discovery with NIP-05. Relays are starting to look at spam filtering (via pay-to-post models mainly).
In the end, most people aren't hardcore libertarians and do want content moderation, centralized discovery, spam blocking... I would really find it interesting if it came about a protocol that actually cared about those things and provided a way to handle them other than a megacorp doing all of it. But all those protocols operate under the assumption that people are okay with seeing really bad things that real people come up with (even CP like commented elsewhere in this thread) themselves under the guise of "full decentralized liberty".
I suspect that's why they all ultimately fail or at least remain niche things. If the alternative to megacorps is this wild west, people will remain in the megacorps' social media.