Maybe give the mods something like that free reign but impose community oversight.

Yeah something like that should be possible. While I completely agree that censorship is shitty and general discussion shoul be allowed and encouraged, I also think in practice this is difficult to realize on such a platform. Some smaller communities (lets say a sceptical atheis community) might be in danger by being completely overrun by a mayority of other pissed of communities with different views (lets say a plethora of religious groups concern trolling, or even "academic theologists offering the same opinions again and again to be "discussed") and as there never are black and white truths out there in the end such subreddits just become battlefields subjected to stupid power- plays, when they were meant to be for a specific community who wants to explore or develop their own argumentations (if you know what I mean). In the end this would just again mainly further and promote opinions that are mainstream anyhow.

Maybe you could see the whole thing like different sports teams, they need to play and train together and not make nonsensical mixes (like we have two ballet dancers training with five football players). But then they can meet in a neutral field of play to compete under fixed and fair rules. This is why I think subs should be allowed have their own rules as long as they are transparent, no trolling and brigading should be allowed, but we can have some battle/ discussion subs where different factions can confront each other.