You are quite wrong about the Vega64 being able to trade blows with the GTX1070 "in some cases".
😉 (but I think that might not be what you meant to type)
For one, AMD drivers mature over time. And for two, the Vega64 never trade blows with the 1070, it traded blows with the 1080 after initial launch.
Here you can see a Vega64
handily outperforming a GTX1080 in almost every test at every resolution, in a more recent review of a Vega64 card:
https://www.tomshardware.com/reviews/powercolor-red-devil-rx-vega-64-8gb,5517-3.html
Of course, you have to be able to handle its 280w power consumption (or more with an OC) for it to make sense.