you are mistaken, Nostr isn't better than Mastodon because it offers unique storage solution. You can backup your Mastodon posts just as well, the difference is Mastodon server owns your identifier, so even if you upload all your posts to your own Mastodon server, you lose your identity (and thus followers).

Nostr commits posts to your public key, and demands that your followers look for you using that key.

of course, it doesn't answer how should your followers find you except by a coincidence of publishing and reading from the same relays.

Pkarr.org offers an answer to that question, but it is not compatible with Nostr keys unfortunately