To be clear, I agree with lemmy.ml on this, but I'm not interested in arguing that stance.
Instead, I think the more important piece of this is that this just further validates the fact that people should be using smaller instances. A more diverse set of Lemmy instances allows defederation to be used more freely as an actual moderation tool.
Someone who posts something an admin on another instance dislikes may see themselves banned from appearing on that instance, which when you have just two or three large instances serving all the content, is an effective shadowban on 1/3rd of the platform. More smaller instances minimizes the impact of defederation, banning, etc.
Anyways, stop only using lemmy.ml, lemmy.world, kbin.social, and lemmy.ee. It's fine to start out there, but find a niche and an instance that fits that niche, then move over there. If you're making a community, consider putting it on a smaller niche instance that would more specifically fit your content and federating it to the bigger instances manually.
We're all power users in here, so it's not as if it's a big deal to move, though apparently 0.19 will have some tooling to assist in that.
The problem is that smaller communities have less content. Yes, they federate with larger communities, but they only pull data every so often. My first fediverse account was on kbin but the fact that it's so difficult to have active conversations there (plus the hard coded invisible porn filter) made migrate to lemmy.
People who crave activity will naturally centralize.