It addresses both scenarios because you can write directly to the big ones.
You can explicitly choose the relay you want to write to, in some particular instance, while your outboxes tell others where a copy of your notes can _usually_ be found.
So, I am writing to a big relay, right now, but a copy is stored in my personal relay.
The only reason why you can write to big ones right now is because no one uses nostr right now. There is no even theoretical incentive for public relays to operate if nostr really becomes something
And no one wants to address this issue. Instead people tend to over engineer 64K relays that are extremely efficient and can serve 256 out of a coffee machine
There is no direct incentive, for public relays, that's true. Incentives don't need to be direct. We run one for documents because we have developed a publishing/reader app. Facilitating the usage of the app is the incentive.
And we will have very large private relays, because of micropayments.
