It is not the margin that is important, it's the fact that it did not get bigger for the AMD cards under conditions that are supposed to favour them - high drawcalls.
This is a problem with AMD's DX11 Draw Calls vs Nvidia's, Nvidia's is just a lot better so the AMD GPU suffers more, it seems to be particular bad with the Fiji Cards, which does explain why they apear to be in some way strangled when considered the size and power of them.