I think there's merit to the argument of 'big corporations can't get things done efficiently' here. I think as you mentioned, for a small scale dev it can be done. I agree, shading could be better across platforms, graphics card manufacturers, even, but that all pales in comparison to a large inefficient corp making grossly over-complex games with staggeringly little added value per hired developer (oh yay another 1mil triangles added to the 100th remake of the same garbage FPS or NFL game, extreme sarcasm).

But outside EA Games e.g., some of the best games I've ever played were written by solo devs in a cross platform engine you may have heard of called Flash. Yeah, not always smooth sailing on Linux, but it worked, pretty well even.