here I would say that there's a myth there, a old legend because it's dfficult to pay attention to a player that have a unique position, and that, is difficult to analyze the sense of his contribution in a way that, we can manage our team, in order to have Key player GK.
But, IMO... the same sensation we have with the Gk can be applied to the defense.... so, I believe thatthere's a sense there, and that, Gks, as a DC can be determinant if r well tested and used.