It's still essentially an appeal to authority. “Good artists copy, Great artists steal” and all that. If an artist is great enough, by definition they're doing transformative things with anything they touch.

For whatever it's worth, I'd say that artists are more qualified to make that assessment than the justices on the supreme court.

>>to state the bloody obvious, if his work was not transformative, it never would have been seen as revolutionary.

that is not at all obvious to me--what is revolutionary in Warhol is not the art but the way people see it, like found art. but if you "found" the art in someone else's comic, and aren't substantially changing the actual image--the actual appearance of the work, the only part that could reasonably be described as being ripped off from someone else... it can be revolutionary without having meaningfully transformed the original, just the way people see it.

disclaimer: I don't have a lot of time for that kind of art, which no doubt biases me.