I don't think nostr fixes that problem, because a relay can delete data if they want to as well.  If we want redundancy and data integrity we can already get that by encrypting data locally and backing it up to more than one place (no nostr required). 

 Yep, but in nostr you have to hash every single item you publish, making checks very easy to implement, compare and reshare. You don't have to think about that before you start using the service. It's backed in.