No social media has global. Even the Internet itself isn't global, anymore.
Everything is overlapping sets covering clusters of elements, with paths to navigate or "hop" from one set to another. And that is the most-efficient structure, as everything is connected as-needed, and can be privatized at-will.
Also, Nostr is not only for publicly-viewable data. Private events will eventually outnumber public. Relays will be incredibly numerous because incredibly cheap.
Good then you explicitly don't want the global discoverablity, and it is very easy for you to claim decentralisation.
And I won't even bother asking what is the difference then between relays vs how Matrix does groups vs RSS feeds etc.. because that is a matter of taste.
As long as the message is clear and the promise of censorship resistant reach is not actively pushed nor passively encouraged l, there is nothing to argue against.
"global" feeds on Nostr have always referred to an unfiltered relay stream, and I've never seen anyone claim otherwise.
I don't think global, or rather "universal", discovery is even possible, so long as someone is free to leave a public network. One person leaving, or taking their communication private, would already destroy universality.
