Run. Your. Own. Mastodon host. Problem solved. Linnode has one click rollouts.
The point is that you have only one Mastodon API endpoint vs potentially infinite Nostr relays for each account you own.
Mastodon is clearly inferior to Nostr when it comes to having a decentralized identity.
The point is you don't have that issue with nostr
This seems like a good area to improve since things like code signing could also benefit. One of the big problems I see is bootstrapping your network initially and also solving the lost phone problem without setting up a system which phishers and spammers would have a field day with.