If this guy is thinking of using public relays he needs to be prepared for being at the mercy of relays if they go down or if there is data loss.

Also as we have seen if we take the blockchain analogy, not everything is a suitable database replacement.

A centralized database will ALWAYS be more efficient than a decentralized solution.

If the use case is using private relays then MAYBE, but then using a REST API and a DB backend probably solves this too.

He needs to ask himself what the goal of the design is. Censorship resistance? Cheap storage? Backups?

Starting from the core questions will lead to not using Nostr as a solution looking for a problem to solve AND doing it poorly.