It's having different communities/magazines (and also groups) that allows you not having to be subjected to the whims of mods, because you can decide which one of those to subscribe to.
We cannot centralise communities because this is not a centralised platform.
Not even in Reddit there's only one subreddit per topic. It's just that centralisation allows you to ignore the existence of those subreddits you don't follow...
What could be done is:
• Having some kind of nomadic identity a la Hubzilla, but for communities. Anything about a topic is immediately copied on any community/magazine about that topic and. This way, if the hosting server of any of those communities dies, the content in the communities hosted there could migrate to similar communities/magazines across different instances on the threadiverse. (This would require adding Zot protocol. I'm not sure this can be done with AP)
• The ability to curate your feed by tags. That way one could see the threads and posts on a topic across instances by following a tag rather than by having to follow different communities/magazines on the same topic. You could also avoid seeing post containing certain tags by blocking/hiding tags.