I am not even certain who thinks it is sensible to compare a 6 year old model to a brand new one?
The amount of technology that has become available in the last 6 years is unreal, and Ford filled the new GT500 with it. Carbon everything, carbon composite everything else, magnesium bits, bigger brakes, aerodynamics, suspension dynamics, better seats, DCT trans, and that bloody engine... oh my. It is an incredible, and incredibly expensive (when fully optioned) machine.
By comparison the Hellcat/Redeye is old news... affordable (you'll see Power Buckaroos again), fun, functional, proven, old news.
But, guess who is moving more units? FCA, that's who.