It seems to me you keep missing the point. Absolutely, there's NOTHING positive for producers by putting each in their own channel. And there's NOTHING positive for paysites to have all their videos on a tube grouped by the paysite name.
HOWEVER, by doing so, there's a lot positive for tubes. First, as mentioned above, it enhances the surfers' experience on the site. Second, they actually end up ranking very high in the search engines, for producer names and paysite names. So more traffic for them.
Now you can argue that if they don't cater to the needs of producers/paysite owners, they won't get content uploaded. Which is pure wishful thinking. There are so many content producers and paysite owners out there hurting for those few sales, it's not even funny. And they lost the sales because of tubes to begin with.
Tubes have the traffic so they can dictate the terms. Worst-case scenario, producers/paysite owners really stop uploading their content to tubes. Fine, they'll just start stealing it again. Which is how they got big in the first place. Sucks to be in your shoes, but unfortunately there's very little you can do about it.