> I used to be very active on USENET and HN is relatively more centralized than a hypothetical "comp.programming.hackernews" newsgroup.

How so? Wouldn't comp.programming.hackernews concentrate discussion under a single heading and also be hosted from a single specific computer? This confuses me even further; I don't understand what you mean by centralization.

>For the phpBB forums where a lots of non-tech people discuss hobbies such as woodworking, guitar gear, etc., the decentralization perspective is the php forums and the centralization is towards big platforms such as reddit / Discord / Facebook Groups.

Surely by this interpretation HN is decentralized. It's a special interest (if relatively broad) forum just like those phpBB forums were. I ask again: is HN "centralized" just because you can't spin up your own copy of the software to use it to talk about gardening?