I'm not saying it isnt, it obviously is. But it's not going to be the next firebase/parsley database with the same performance profile that you can get for free with the extra open protocol magic. You should definitely build your own proprietary, optimized backend but the point is that the "less optimal" nostr req is still there to not gatekeep data flows
Discussion
Yep I'm aware of the tradeoffs. Not everything should be free, and just like NIPs could be optional. Proprietary backends are not swappable, at least not as easily as a relay
As far as data flows its mostly clients querying relays for small subsets of data, effectively using them as open APIs anyway. For relay to relay negentropy is more efficient