A big selling point of Bluesky is algorithmic choice. There are three default feeds, one is "following" which is exactly what you said. If you swipe to the right you get "Discover" which is a lot like the "For You" Twitter feed. Finally there is "Popular With Friends" which is what it says on the tin.

If you don't like those, anyone can develop a feed algorithm and anyone can subscribe to it, so you can have topic based feeds like "Science" or you can have feeds that just change the way the feed behaves like "OnlyPosts", which is the following feed but with no reposts or replies.

so... what exactly IS Bluesky good at then?

It's good at showing you the posts from the people you follow. The quality of your feed is entirely up to you.

That's exactly what Twitter does. Why is this a differentiating feature?

Fewer Nazis in your replies is the big one.

Has this changed recently? When I was on Twitter a few years ago I often missed posts from my friends because the algorithm didn't show them to me. Same when I posted, often my friends didn't see it.

I don't follow anyone though. I don't know anyone using Bluesky, and I have been unable to find anyone worth following in any feed.