let's put aside self-hosted solutions—they're only for about 0.05% of the population, the most tech-savvy guys. but even for them, most fediverse software isn't as user-friendly as it should be. e.g. mastodon is overly complicated and difficult to update and manage, even for those with technical skills.
for everything else, I would agree with you, if most fediverse software supported a decent way for users to own their identity and seamlessly transfer their account, along with all associated data, without needing authorization or cooperation from the current server’s admin. it would be like nostr relay—they’re truly support actors.
as it stands, casual users are free to choose any instance, but their account is ultimately at the mercy of the server admin.