That's not true. Mastodon replicates all your posts to a bunch of other servers you don't control by design, which makes them harder to erase.

It's no worse than normal internet publishing, but it doesn't magically solve the erasure question.

Yep. And you still de-anonymise yourself with Mastodon when you buy hosting and a domain. If you use an existing provider, then you're back at square one and living in hope that the provider doesn't keep logs etc, or just decide they don't like you.

Nostr fixes both of these. So whilst you're at the mercy of relays storing your data, you can at least be anonymous.