I didn’t find any posts saying what you have claimed other than your own. What I have found referring to increasing the gpu load for improving performance refers to smoothing out stutters, not increasing fps. Even @Grabber523 seems to agree with this in this post.
The frame time of 40ms on the CPU means it’s taking 40ms to complete the frame calculation. Those calculations are the same regardless if you render in 1080p or 8k. If it’s 40ms at 1080p, changing the render scale doesn’t cause the CPU to suddenly complete the same operations in 2.5ms simply because there’s 16x more pixels being rendered.