BF4 in dx11 on my 290x was running at ~80fps@1080p everything ultra (cpu 3930k@4ghz). When mantle patch came out fps jumped to 120 at same settings. Anand tests show that 980gtx was getting 90fps. So I got 30fps over 980gtx. how is that in your waffle world not a substantial improvement???
And my system was considered top of the range where AMD was telling everyone that it would get least of the boost. How is 40fps extra - a small increase?
Bf4 at 1080p ultra settings on my 780 got 100+ odd average fps with a 3570k at 4.2 so as I Said nvidia's competing cards on dx11 were just as good as mantle on amd's in bf4.
I have nothing to say about mantle helping Amd's own cards because it did.