Also: X uses 1 connection to 1 server. Or at least not many. Nostr sets up many?
Indeed. Though I'd hope that the redundant connections are only downloading the JSON notes and not also redundantly downloading multimedia content.
I think @primal cashing relay helps here. Not sure about how other apps do it. But I have a feeling that they do download redundant notes. Unless the app refreshes the filter parameters after each incoming note? But it must be media that creates this issue, not text notes even if there were redundant downloads.