Apples and oranges. Nostr is a relay protocol, much like HTTP is a hypertext protocol.

Twitter is built on top of HTTP, but we don't say HTTP is trying to replace or improve Twitter.

Nostr is also built on HTTP, but it specializes in something different: transmitting notes and other stuff between users via relays.

Protocols are simply tools—like APIs or libraries—that enable applications to function. Twitter could integrate Bitcoin, and it could integrate Nostr, too!