If the descentralization of social networks continue, we will have to prepare for the eventual rise of the instances wars, where people will start to fight about which instance is better and which one is weird to be in and so on, but that’s for the future of us all.
(Disclosure: Assuming you’re talking about Usenet newsgroups here.) They are, and I’d say it’s reasonable to call it an echo chamber. Anything to do with politics tends to border on extremism less common on the “regular” internet.