I know that is what Nostr people think, but it is not sufficient. Yes, you should keep copies of your data, this is true of any data you care about in any use case, everywhere. That doesn't give you a way to be censorship resistant on the web, social media, search, etc. Your backups just ensure you can try again, which was true before Nostr. But 99% of people don't want to run a server, and 99% of popular people wouldn't be able to scale their personal server to be able to serve many people efficiently.