Mastodon is more open than you think.

You made a post to attempt to dispell what you consider a misunderstanding about BlueSky, yet your comment suggests you dont understand the Fediverse.

Well, that problem also exists with mastodon.social

No, it doesn't. There are thousands of instances, some with hundreds of thousands of users. If you sort the instance list by active users, the population spreads out even more, because smaller instances have more active users.

and a lot of the actual fediverse.

Wrong again. Lemmy.world is about 30% of Lemmy, and less when you include Mbin, PieFed, etc.

Its less distributed, but its still decentralised.

I run a Fedi instance connected to hundreds of others. If one, even a large one, defederates me, it does not cut me off. If I ran a PDS, I'd be connected to BlueSky, and they can do what they want.

You are rationalizing this to yourself because you like BlueSky.

That's at a very different level. With dot social it's about a quarter of the active users on the fediverse, whereas bluesky is probably something like 95% centralized in practice. It seems to keep improving, but right now it's basically impossible to use without mostly interacting with bsky.