Things like this can often be assessed on a macro level. When you start to get the number of users sites like Facebook have and sites like Reddit claim they have, you end up with content that's reflective of a broad sample of society. You do have that on Facebook, you do not have that on Reddit.

I suspect Reddit is intentionally overcounting by doing things like counting multiple devices as different users, multiple accounts as different users, making minimal efforts to remove bots, counting dynamic IPs as distinct users, and so on. You could even count API callers as users, but that is stretching the limits of plausible deniability. The thing is - their content isn't reflective of the popular town bar, it's representative of an insular clubhouse with some small rooms in the backyard for 'normies.'

Reddit is a bunch of bar districts in a large city. You can find any sort of bar you want. Some of the bars you'll love. Some of them you'll hate. Some of them will make you say "what the hell is any of this?"

It's an almost infinite variety. Fractal even with how many subreddits are the results of splits from an older subreddit.

No. I'm very specifically saying (contrary to your implication) that it's the management of the bar which is the problem

HN loves to do this. "Platforms are mirrors held up to society". No, not always. Sometimes there really is unnecessary executive top-down control