Expecting a normal user to notice the differential between Primal’s Nostr feed and the one on the network is not realistic. So is expecting a normal person to tinker with settings, know what a caching server is and knowing how to locate and replace it. Whatever the default is, that’s the setting that is staying for virtually all users except a tiny fringe forever.
It seems to me that Primal is repeating the essential problem with federation that Nostr was solving in the first place. In a federated system censorship becomes trivial because ever since conversation goes through gmail.com or bsky.app — the concentration of large numbers of people on a single server creates perverse incentives over time. If Nostr ever becomes popular and the most popular client is reliant on a single caching server, the operator will be ordered by courts, domain registrars and registries, CDNs, BGP peers, and app stores to filter it. Or the board will just elect new people who are censorship friendly because it is the only way to be commercially viable and get ads that pay well.