Congrats, you've uncovered some of the basic laws of creating functioning communities online.

I've personally used the success of a few sites to discover what sets up other forums for failure, and therefore what rules can be inferred to better manage other places.

One of the major converse implications of what you've written is that generalized subs, and especially those which allow politics of any type, will degenerate over time.

Or in other words, generalist subs have a minimum/negative of conversation that has to be fought against - and the best case is a zero sum conversation, or slightly positive.

In contrast vector type subs (places where the conversation is directed, a goal that has to be achieved) have a maximal/positive type of conversation that can be attained.

This in turn has horrid implications for most of communication online.

1) Subs which have a subject filter - in particular challenging personal or mental tasks which can't be faked - to intelligently partake of conversation do better.

a natural filter also keeps out posers, who are not a problem initially, but end up eroding the community from the inside in the long run.

DF has one of the harder filters to get through, and has a small enough community that its possible to manage.

2) Vector topics do better than static. If you are forced to ACT or have goals and move towards something, that sub does better over time

3) generalist subs do the worst