Bluesky’s more like an aspirationally decentralized platform, you can keep your own data on your own server and use your own domain name as a user name, but most of the rest of it is “centralized, but we’re designing it in such a way that we can open it up later.” Even then, though, it’s heavily influenced by the original idea of “let’s make something decentralized that Twitter can switch to once it’s worked out” which means that even when they do open things up, it’s likely that a lot of Bluesky will only be practical at “big tech company scale” to run yourself, whereas Mastodon or Lemmy you can just spin up on a server and it’ll be fine until you get a lot of users.