He's obviously not referring those subreddits. If you read the piece he's talking about subs like r/news, r/politics, r/worldnews, etc.

If you don't think r/politics is an echochamber then I don't know what to tell you.

r/fatFIRE was a great subreddit I used to visit frequently but it grew very quickly over the past few months and the mods haven't scaled accordingly. The moderation has gotten really, really bad over the past few months and the sub is now just filled with dumb posts like "what handbag do rich people buy"? It used to be far more technical, interesting discussions around real estate investing, taxes, etc.