To be honest I have not tried Mastodon. I wanted to follow mastodon users but never could figure out how to join a relevant server. I have not revisited since.
Granted Nostr is not the easiest to use either.
That said, Nostr is more than just a messaging Protocol. Devs are looking for ways to expand this. For example, one idea is to use the Nostr network to replicate go fund me. Another example is #[5] offering millions of sats for someone to create a decentralized replacement for GitHub.