Personally, I think any decent game developer should be testing and optimising their games for chips from all major vendors.

It doesn't matter if the 80% running Intel chips are happy because if your game runs like a turd for no good reason on the chips from the other 20% they will be the most vocal and will tank your game ratings.

The only information that can be safely gathered from the steam hardware survey is that "some people use Intel CPUs, and others use AMD CPUs" and "some people use Nvidia GPUs and others use AMD GPUs". Which would mean you should, ideally, optimise for both vendors for both CPUs and GPUs.

Sigh... in an ideal world, anyway *cough* without general anti-consumer/anti-competition shenanigans *cough cough*