I'm of the mindset that agrees that Star Fox Zero is not a good-looking game, and in reality, the core issue really IS that they're rendering the same screen space twice at 60 fps. That is a HUGE drain on power.
I personally think a game like Star Fox does NOT need 60 fps, however (and I am well aware this is Platinum Games' target goal all the time), and I actually think a drop to a solid 30 fps would do this game wonders in pleasing the eye while maintaining enough fluidity as to not hamper the experience.