You always own your notes on Nostr, Not so on fedi. Outbox will solve a lot of these issues, once the major clients (Damus & Primal) implement it that will be a huge boost. Nostr is still early in development (3 years compared to mastadons 10), so there's time to develop other ways of transmitting notes between users. I remember using identi.ca 15 users ago, federated networks have come a long way since then. Nostr isn't in its final form either.