They messed up when they made sub-reddits. Sub-reddits are a harmful combination of community and content. Popular content becomes a huge community, and all of the issues based on Dunbar's number happen as a result, which includes abuse of powers from the admins. Instead of using sub-reddits for content you should have tags. Communities should never be bigger than 150 people, and should not be limited to a single idea, in much the same way that Hacker News is aligned generally towards hackers. You would then build up communities of communities, where you would be beholden to your own community and the communities could only moderate outside of their community at the community level.

From there you only have to do a decent job like TikTok has done of content discovery to allow new content to thrive, and from comments on that content allow people to find better communities.