In the Fediverse your account and identity is linked to a domain (e.g. you are @someone), and you can’t move that account somewhere else. You can’t even change the domain of a server, because all the accounts on that server would be known by a different domain and be treated as separate new identifies. In Bluesky your identity is basically a random number, it’s shown in the URL of a profile page for example. You can link that to a domain temporarily and get a nice user handle, but you can always move to another domain later. That means you can migrate between servers and keep all your friends and followers, something that’s currently not possible in the Fediverse.
The thing about schemas is a technical detail, not really any consequences for users. Then there is a different format for user handles, so the Bluesky people don’t like the double @ signs for those.
The last thing is about how you don’t just pick one server/instance in Bluesky, instead you can pick different servers for different things. One server hosts your account, but a few others can fill and sort your news feed, block spam for you or let you search through content. It’s supposed to create an open ecosystem for these services, and allow you to keep your account on a server that offers none of these by itself, e.g. a small home server. Of course there is nothing like that in the Fediverse, you pick a service and a server, and that’s it.
I have to say Bluesky looks extremely interesting from a technical perspective, there’s just the fact that it’s completely dominated by the official server right now. People can create their own servers though, so we’ll have to see how it evolves.
Bluesky and Mastodon users are having a fight that could shape the next generation of social media (techcrunch.com)