“Low and slow” does not mean “as low and as slow as possible.” The idea of “low and slow” is to “cook” the collagen (the primary protein in connective tissue and what makes meat tough) to get gelatin. That both tenderizes the meat and retains moisture. Gelatin is what makes something “lip smackin’”! That reaction requires moisture, and one of the best cooking methods to make it happen is braising.
The idea behind wrapping is to achieve something of a braise. It also slows down evaporation. That keeps the meat from drying out on the pit, and it gets you through the plateau. In “Modernist Cuisine,” the authors finally showed us that the plateau is pretty much due to evaporative cooling. In other words, you aren’t so doing much cooking during the plateau. Instead, you are spending a bunch of time and fuel to dry out your final product. Or, you can wrap the brisket and get through that point (and get a better product).
Just like ribs, brisket’s high ratio of surface area to volume makes it particularly vulnerable to evaporative cooling. That’s why we wrap 'em both.
As for pink butcher paper v. foil? I’ve used them both and do agree that butcher paper sets the bark better than foil. It seems to allow enough evaporation to set the bark but not so much to stall the cooking. However, I get the same result just by opening up the foil when my brisket gets close to finishing (not on the bottom, mind you, but that’s the point, and I’m not as concerned about the bark on it). Since I’m only cooking 1 or 2 briskets at a time (instead of the 100 or so that Franklin’s cooks in a day), I don’t mind the extra trouble. Of course, it’s not like wrapping with butcher paper is much trouble.
So, I’m quite happy using either. Whatever is in front of me will do. If Aaron Franklin says that pink butcher paper is better, then I believe him. The man cooks more briskets in a few days than I’m likely to cook in my lifetime, so I’m going to listen to him. However, in my situation, it doesn’t really make much difference.