bigjohnny :
i want to play current games like dishonored 2 watch dogs and old games like battlefield 3 batman arkham origins gta v at 1080p max settings 60+fps
rather than looking at the API you should look at the game itself. DX12 is quite complicated matter. AMD usually get better with DX12 but it doesn't mean RX480 will
always be better than nvidia in DX12 based games. take gears of war 4 for example. the game is DX12 exclusive but due to the nature of unreal engine 4 and game developer themselves are in more close relation with nvidia the game actually faster on 1060.
http://images.hardwarecanucks.com/image//skymtl/GPU/GTX-1060-UPDATE/GTX-1060-UPDATE-75.jpg
as for the game you mention dishonored 2 and watch dogs 2 are faster on nvidia hardware (well since both actually nvidia sponsored tittle) as shown by the test made by TPU:
https://www.techpowerup.com/reviews/Performance_Analysis/Dishonored_2/4.html
https://www.techpowerup.com/reviews/Performance_Analysis/Watch_Dogs_2/4.html
for battlefield 3, batman origin and GTA V RX480 and GTX1060 will do very well at 1080p if your aim is simply want 60FPS since both card able to exceed that though when if the frame rate is uncapped 1060 definitely faster in battlefield 3 and GTA V as shown here:
https://www.techpowerup.com/reviews/Zotac/GeForce_GTX_1060_Mini_3_GB/17.html
https://www.techpowerup.com/reviews/MSI/GTX_1060_OC/8.html (the result for this is coming from much older bench because this is the last bench TPU include BF3 in their test suite).
with batman origin you can enable nvidia gpu PhysX if you use nvidia card. i'm saying all this because some people only care about constant 60fps and did not care beyond that. and seeing the price already much more stable right now than it was at launch RX480 can be had cheaper than 1060. so RX480 can be more compelling choice than GTX1060.