[krapp]

If your thesis is that simply having separate threads with different topics counts as being decentralized, then Reddit is decentralized because it has different subreddits for different discussion topics as well as different threads. And literally every other social media platform counts as well, for similar reasons.

The "center" that matters in this context is the server and owning entity, not the taxonomy of the content. Decentralized platforms aren't owned and operated by a single entity, centralized platforms are. You can't just spin up a new instance of Hacker News with different moderators and just federate with it, because "Hacker News" as a network is entirely owned and controlled by YCombinator. Not so with, say, "Mastodon."

Also yes unfortunately there are already multiple blockchain-based social media platforms.

[immibis]

No, you are on a separate SITE with different topics. One or more sites exist for each topic, run by different people. They all compete, with no obvious single center. You are on Hacker News to talk about technology, mostly software. To talk about mostly networking, you could go to #networking on Libera. To talk about raising fish, you could go to I don't know where. Let's stick to those two examples I do know - why do you think that Hacker News is "the center" of the non-Reddit forum ecosystem, and #networking on Libera is not "the center"?