I think Apple using their own processors on Macs will make their sales much higher than today.
(assuming they have the same performance boost as iPad pro)
It really doesn't matter! The real question is, why can't I play Overwatch on a Mac? Talk to companies like Blizzard, find out and fix it already. If you can make your own chip to make that happen, cool! I mean... I kind of doubt it, but I don't care if I'm wrong.
Unless Apple's custom GPU is going to leverage AI to achieve real time Ray tracing and support NVIDIA's proprietary CUDA architecture it's a no contest. But then again it's a no contest anyway since VFX and game industries already shifted to Windows because red shift, v Ray, I Ray octane and every other GPU accelerated renderer requires CUDA. Apple's no longer a competitor in pro graphics so even if they do go NVIDIA now it's too little too late.
NVIDIA already has expertise integrating their graphics technology with ARM-based processing (the Shield). No need for Appe to reinvent the wheel, although I suspect that they will go that route!