I don't think that's actually true.
GP100 has all the FP64 cores, which add nothing to gaming performance but increase heat and decrease clockspeeds.
The full unlocked core only has 3840 FP32 cores, vs 3584 on the Titan XP. I wouldn't be surprised if GP100 can't hit above 1800 MHz, in which case the GP102 core probably ends up faster (or equal) in gaming.
GP100 has 256 more CUDA cores, plus HBM2 memory. It would annihilate the Titan XP, but it's not available for us mere mortals
