Caporegime
I think if you spend the time and actually code around the limitation of the architecture, you do get more performance, just as you get more if a developer puts in the time and codes for Mantle/DX12/Vulkan with GCN. That doesn't happens often on PC (and to be honest, considering AMD's marketshare, no need to bother much), but on a consoles it can circumvent up to a point the bottlencks.
You can also see that in consoles titles where the devs put that extra effort.
Yes but the difference in performance between navi and vega is nothing to do with developer coding