I would not call it that is the case. 250W GPU from AMD has 6 TFLOPs of compute power. 250W GPU from Nvidia has 6.1 TFLOPs of compute power.
275W GPU from AMD has 8.2 TFLOPs of compute power, and there is nothing from Nvidia that can be compared to this. Games are different thing. DX12 shows that compute power will reflect gaming performance in future. Other thing is that, with current drivers, and reference models of GPUs AMD get performance lead in every price/performance bracket. It leads in 4K, it leads in 1440p it leads in 1080p. I have written this over, and over, and yet people tend to still say the same not actual things about the GPUs that are on the market.
Only benefit for Nvidia at this moment is CUDA locked software. But it is possible to run CUDA on AMD GPUs without any penalty... So guess what will happen?
P.S. There is one thing that will be shining in Pascal. Properly fed ROPs. 96 of them to be precise, coupled with HBM2. It will be VERY interesting to see the numbers but I think it will be first time when we will see that type of front end on any GPU.