It would be more fair to say that they approached the problems that need to be solved in federation with different priorities than ActivityPub.

People on ActivityPub based networks seem to want more independent niche communities with their own control over the community's content.

The AT protocol makes it so that the users, themselves, are able to control their content.

Philosophically it's an alternative to the Nostr protocol more than ActivityPub, and I don't know that you could wedge their prioritized solutions into this protocol's ecosystem.

While practically there are limitations to Bluesky federation (the cost of running a general purpose relay is not likely to be user supported), there is only one piece of their tech stack that currently is centralized (as far as I'm aware).

Sadly itself the ID generation and authentication portion.

And I wish we had a solution to that problem in the ActivityPub fediverse. There is no way to keep yourself if your instance is shut down, so you don't have any control over yourself as a user.

If that problem were solved in a way that still enabled communities the way we do I would prefer it to any of the current options.