A lot of people’s research about bluesky is just the “How decentralised is bluesky really?” article by Christine lemmer-webber.
While the article was good at the time, and still has some relevant parts, a lot has changed since then.

Namely, relays got cheaper to run (about $30 a month).
Right now the problem is that everyone uses bluesky’s infrastructure (and PDS migration is a bit spotty, but bluesky is working on that).

Also: AP is pain. The spec was rushed and doesn’t include a lot of key details. Atproto was better thought out (at least in my opinion).