You sign the notes with a cryptographic key. It doesn't matter where they are stored, they can't be tampered with. You can store them on any relay and your followers can verify they were yours.
Discussion
Then post them to multiple relays. The chance of every relay blocking your notes is low. If that happens run your own relay.
"run your own relay" yes- you are making my point.
It's the same as hosting my blog, my own YT etc. It's the only way to be self-sovereign, but with no reach and unlikely to be discovered.
We had open protocols before to access dispersed self-sovereign notes and blogs (RSS), yet it failed to catch on and people gravitated to the big platforms Medium, Substack etc.
Nostr is also essentially the set of "relevant" central relays which everybody subscribes to to find and be found. We trust them to continue to behave honestly.
That's why using clients that support the outbox model are important.
The only thing better is for every computer on the network to have a copy of your shit post, like on a blockchain. But is your shit post important enough to require such a data inefficient storage solution.