Bluesky's claims of being decentralised were always way way ahead of the de-facto reality of it. That's not the same as Mastodon.

It has been a "rallying cry" but it doesn't stand up to much scrutiny of how Bluesky actually functions: an "open protocol" with one central server means little. Maybe this will change at some point in the future, and maybe it is changing, see https://blacksky.community/ . But this is not the same as Mastodon, where it's been that way for a while.