NVIDIA is basically the only GPGPU game
NVIDIA GPUs are definitely the go-to these days, but the world's most powerful supercomputer is using AMD GPUs. I wouldn't be surprised if AMD picks up speed (though they probably won't beat or meet NVIDIA). NVIDIA got started way sooner, so the fact AMD is behind is only natural.
Engines for linear first person shooters aren't necessarily good for Skyrim-scale RPGs.