Bluesky advertises itself as an open network, they say people won't lose followers or their identity, they advertise themselves as a protocol ("atproto") and because of that they are tricking a lot of people into using them. These three claims are false.
protocolness
Bluesky is a company. "atproto" is the protocol. Supposedly they are two different things, right? Bluesky just releases software that implements the protocol, but others can also do that, it's open!
And yet, the protocol has an official webpage with a waitlist and a private beta? Why is the protocol advertised as a company product? Because it is. The "protocol" is just a description of whatever the Bluesky app and servers do, it can and does change anytime the Bluesky developers decide they want to change it, and it will keep changing for as long as Bluesky apps and servers control the biggest part of the network.
Oh, so there is the possibility of other players stepping in and then it becomes an actual interoperable open protocol? Yes, but what is the likelihood of that happening? It is very low. No serious competitor is likely to step in and build serious apps using a protocol that is directly controlled by Bluesky. All we will ever see are small "community" apps made by users and small satellite small businesses -- not unlike the people and companies that write plugins, addons and alternative clients for popular third-party centralized platforms.
And last, even if it happens that someone makes an app so good that it displaces the canonical official Bluesky app, then that company may overtake the protocol itself -- not because they're evil, but because there is no way it cannot be like this.
identity
According to their own documentation, the Bluesky people were looking for an identity system that provided global ids, key rotation and human-readable names.
They must have realized that such properties are not possible in an open and decentralized system, but instead of accepting a tradeoff they decided they wanted all their desired features and threw away the "decentralized" part, quite literally and explicitly (although they make sure to hide that piece in the middle of a bunch of code and text that very few will read).
The "DID Placeholder" method they decided to use for their global identities is nothing more than a normal old boring trusted server controlled by Bluesky that keeps track of who is who and can, at all times, decide to ban a person and deprive them from their identity (they dismissively call a "denial of service attack").
They decided to adopt this method as a placeholder until someone else doesn't invent the impossible alternative that would provide all their desired properties in a decentralized manner -- which is nothing more than a very good excuse: "yes, it's not great now, but it will improve!".
openness
Months after launching their product with an aura of decentralization and openness and getting a bunch of people inside that believed, falsely, they were joining an actually open network, Bluesky has decided to publish a part of their idea of how other people will be able to join their open network.
When I first saw their app and how they were very prominently things like follower counts, like counts and other things that are typical of centralized networks and can't be reliable or exact on truly open networks (like Nostr), I asked myself how were they going to do that once they became and open "federated" network as they were expected to be.
Turns out their decentralization plan is to just allow you, as a writer, to host your own posts on "personal data stores", but not really have any control over the distribution of the posts. All posts go through the Bluesky central server, called BGS, and they decide what to do with it. And you, as a reader, doesn't have any control of what you're reading from either, all you can do is connect to the BGS and ask for posts. If the BGS decides to ban, shadow ban, reorder, miscount, hide, deprioritize, trick or maybe even to serve ads, then you are out of luck.
Oh, but anyone can run their own BGS!, they will say. Even in their own blog post announcing the architecture they assert that "it’s a fairly resource-demanding service" and "there may be a few large full-network providers". But I fail to see why even more than one network provider will exist, if Bluesky is already doing that job, and considering the fact there are very little incentives for anyone to switch providers -- because the app does not seem to be at all made to talk to multiple providers, one would have to stop using the reliable, fast and beefy official BGS and start using some half-baked alternative and risk losing access to things.
When asked about the possibility of switching, one of Bluesky overlords said: "it would look something like this: bluesky has gone evil. there's a new alternative called freesky that people are rushing to. I'm switching to freesky".
The quote is very naïve and sounds like something that could be said about Twitter itself: "if Twitter is evil you can just run your own social network". Both are fallacies because they ignore the network-effect and the fact that people will never fully agree that something is "evil". In fact these two are the fundamental reasons why -- for social networks specifically (and not for other things like commerce) -- we need truly open protocols with no owners and no committees.