I would just add to all this that there are very few players who are really “purely” anything, as the many astute examples here point out.
However if you’re trying to categorize players in a way that might help understand the differences, one thing that is more consistent is the baseline setup. For example, however you describe George Benson’s picking system, it is clear that his baseline arm setup is a supinated. Same for Albert Lee and Zakk Wylde and Marty Friedman. These players all make various different picking motions, and they sometimes become pronated in the process. But they almost always start with and return to a supinated setup.
And of course supinated setups very often correlate with downward pickslanting. But it’s a broader category. If we’re doing family trees, I would connect all the supinated players on one side of that tree, and all the baseline pronated players (McLaughlin, DiMeola, Andy Wood, Molly Tuttle, etc.) on another branch.
That might be more helpful for you in terms of thinking about your own setup, and what you’re going to need to do to play various lines, than thinking specifically about “pickslanting”, which may or may not always be a part of that equation.