because I think the post assumes that the GPU is always using all of its resources during computation when it isn't. There's a reason why benchmarks can make a GPU hotter than a game can, as well as the fact that not all games pin the gpu performance at 100%. If a GPU is not pinned at 100%, there is a bottleneck in the presentation chain somewhere. (which means unused resources on the GPU)

You aren't going to use these features on extremely old GPUs anyways. Most newer GPUs will have spare shader compute capacity that can be used for this purpose.

Also, all performance is based on compromise. It is often better to render at a lower resolution with all of the rendering features turned on, then use upscaling & frame generation to get back to the same resolution and FPS, than it is to render natively at the intended resolution and FPS. This is often a better use of existing resources even if you don't have extra power to spare.