One of the BTK documentaries did a similar analysis (maybe the same one you referenced?) and came to the same conclusion.
The authenticated tintype (which some actually doubt is really BTK) shows a rather longish and somewhat pointed chin. This matches several contemporary descriptions of him.
Brushy Bill had a very flat, almost square jawline. That by itself is enough to conclusively say the two were not the same person.
This particular image excited me initially because it seemed to have some possible provenance and because in my opinion, the match is a possibility given the limitations of the images we are working with. Unfortunately, the provenance claim seems to have died and so too does my excitement. :(
I think the two photos (1 tintype) look quite a lot alike. Several years ago Scientific American or the Smithsonian Magazine did an analysis of the BTK Photo and a photo of Brushy Bill of Hico,Texas... more