And this unity destroyed them because one set of rules for all groups just doesn't work, ever. So now the forums move there, then lose all content as the people actually involved get pushed out of reddit by increasing gentrification and facebookization.

This does happen but I think the reason for that is that Reddit's effective SSO across forums means that there is much easier access to niche communities which means that the mops take over the geeks quite easily.

Reddit is pretty good about letting arbitrary rules prevail so I don't think it's the unification of rules.