Until you can show me something made by AMD that can compete with a GTX 1080 without consuming close to 500 watts, I call full on shenanigans to your post. You want to compare a 30w APU to a full blown next gen console GPU? LOL.
Fenguang is a Ryzen powered apu and is VERY impressive for the power draw. The One X is not Ryzen powered but still does damn good for the power, somewhere between a GTX 1060 and GTX 1070. Having a Vega 56 - like card on one of these APUs seems very doable.
edit - if the just stick with Polaris and and made it faster and bigger while using 7 mm with GDDR5X, it would make things MUCH easier for game developers. It is important to look at it from all points if view.