[rhizome]

Quality of the site as a whole, both subs and comments.

Again, you're assuming that the presence of additional advertising will have no effect on the content. Perhaps your example webboard always sucked, you know?

One additional way to look at it is to gauge whether your webboard is more popular and/or more highly trafficked than its related subreddits. This last point doesn't necessarily speak to content quality, but it does relate to the relationship and motivations of its community.

A tenet of advertising is to maintain a blindspot for self-reflectivity, to assume that everything would be the same whether they were present or not. Leaving aside the economics of production, for a simple example of TV shows, a lack of advertising would enable longer shows and thus more content, which is what people presumably watch these shows for. A negligible number of people watch TV only for the advertising content, and I think we can agree that a station that is only comprised of advertising would not be very popular. QVC will never get the ratings that "Duck Dynasty" does, much less one composed entirely of 30sec spots.