Personally I still think Google Plus got a lot of things right. It was a very pleasant place where people had real, meaningful discussions, and was quite unlike Facebook or Twitter. Nothing else I've tried since its disappearance had quite the same sense of content and community.
What exactly made it so different is hard to say. Was there something about the way you organised your friends into circles? You could share things either publicly or to specific circles, or to your "extended circles", which meant all your circles, and it was readable to their circles too I think, but it still wasn't completely public.
But it could also simply have been the kind of crowd it attracted. Maybe it was helped by the fact that it wasn't the biggest. It also had a ton of extra features (agenda and hangout integration) that a lot of people loved, but unfortunately Google kept messing with that.
Of course it was still corporate, and a real social network needs to be open source and federated, like the Fediverse. Maybe another thing to consider is: is ActivityPub a suitable protocol? Does it do everything we need? Does the sharing between conceptually completely different social media on the Fediverse work well?