Reddit Migration

Frankly, you're incorrect. It's an incredible pain in the neck to try and deal with the Fediverse beyond local content.

What issues have you specifically noticed with this? I've only seen a few - the main one is sometimes it's hard to find magazines from elsewhere unless you already know the name of it and the instance it is on (but folks are creating websites to help others find this, so this is a problem being solved right now). The other one is that sometimes federation is slow, so posts and comments on the hosting instance can take hours to show up on another one. But there are technical fixes to this as well (I'm thinking that maybe the next version of activity pub should include a pull action, so other instances can ask for the latest content on behalf of their users from the hosting instance).

Without better community merging or centralization, browsing instances becomes no different than dealing with having mail on three or four non-multiplexed BBSes,

I wasn't around this far back. Can you elaborate on this a bit? What's the issue with "having mail on three or four non-multiplexed BBSes" ?

or talking on forums before we had tabbed browsing. It's incredibly annoying, and pushes people right back to centralized systems.

This I remember well. Sounds like you are trying to create an account on each instance and are constantly logging out of one and into the next to keep up on the latest posts and comments. This .. is not really the way to do it.

Yes, active users continues to grow - on already dominant platforms. And by that I mean KBin.social as a platform,

Don't confuse terms. kbin.social is an instance, the platform is kbin the software.

not all KBin instances;

Actually it's well understood that kbin.social is getting too large and it's not good for instances to get this big in general - so it's kinda a good thing that other instances haven't exploded as much. See https://kbin.social/m/RedditMigration/t/122067/Jim-is-invading-the-finer-things-club-aka-kbin-social-is and

or Mastodon.Social,

I'd argue that this is a technically a different platform - microblogging vs what reddit/lemmy do. But by the magic of federation we get both in kbin.

or even Lemmy.ML.

There are problems here with this instance that go far beyond what you are saying. But that's the nice part of federation - even problematic owners can be dealt with. Can't say the same for a centralized service.

Yes, there's not a singularity yet,

Why use this term? What does it even mean in this context? A singularity is a term from physics and represents when the existing rules break down, like in a black hole (collapsed star).

but even this limited plurality shows that it's a pain in the neck to deal with the Fediverse as a whole, so pick your local poison and go for it.

Again, this suggests you don't really understand federation. Barring one problematic instance, there aren't any serious issues accessing all the instances you mentioned from, say for example, kbin.cafe

You and I will have to agree to disagree on this.

Certainly.