Reddit is a tool for promoting groupthink and is quite easily controlled. Some of it is organic where the mob mentality is grown through upvoting and downvoting independent thoughts and unpopular opinions. Some of it is brigading and bots from private organizations and governments aimed to shape that public opinion. And some it is from mods in a form of super powering that upvote and downvote.
I do not believe it is that controversial to suppose that most non-niche subreddits are being manipulated by one of more of the above.
Maybe, but... You're comparing it to facebook. There's whole countries for whom internet = facebook. Facebook could have very well been a major element in 2016 USA elections. It has a magnitude more users than reddit (although the number is gradually getting closer). It's much more opaque than reddit, who knows what really goes inside of it.
I mean, it's Facebook. If you're arguing that something has bigger reach than Facebook, you need more than those arguments.
I do not believe it is that controversial to suppose that most non-niche subreddits are being manipulated by one of more of the above.