>Graphics programming skill (by 'skill', I mean being able to write a shader pipeline that both satisfies the art direction and performs well), on the contrary, is very deeply tied to a good understanding of hardware.

I'm not entirely sure I agree in the modern day sense. Especially if our analouge is webdev. So much of industry is using UE and Unity that you probably can be a "graphics programmer" professionally without ever knowing what a vertex buffer is (only slightly exaggerating). Your ultimate job is either to a) make images look better b) make images run faster or c) make sure images can get put into the engine properly. And a high level understanding and implentation of shaders/texturing concepts and understanding which settings run slower on those engines (even if you can't explain them in detail) can get you pretty far in those regards.

you're certainly SOL once you move out of your engine of choice, but you can definiely be productive enough to get hired if you got a foot in the door.