> What's the difference you're pointing out?

They don't equally apply.

> (in both cases you can host your own thing if you like), and the latter (downside) applies to Bluesky when you sign up with the official server right?

You can host things, sure, but atproto (this is really more about the protocol than the application layer) has true account portability, whereas Mastodon does not. Moving your account on Mastodon account has multiple options, all of which are closer to redirects: https://docs.joinmastodon.org/user/moving/

This all also requires cooperation from your host; if you're kicked out, then you can't do any of this. A profile redirect only stays up as long as that host is up.

Whereas with atproto, you can move between PDSes, and nothing will change with regards to your social graph. If your old PDS kicks you out or dies, you can recreate all of your data onto your new PDS by replaying it off of the relay.

That is, with Mastodon, your identity and your data storage are linked, so changing your identity requires changing your data storage, and changing your data storage requires changing your identity. But with atproto, these two things are separated, so changing one does not require changing the other.

Even if you sign up via bsky.app, there isn't even one official server: they partitioned their userbase among a bunch of different PDSes.