The increased CPU/GPU usage is expected, which is what I was trying to describe in my first comment near the top…
- GPU memory usage is higher due to virtual framebuffers being larger than the physical screen resolution.
- GPU fill rate will be lower if Xorg or the driver has to recomposite every frame. This hurts general performance and power usage.
but also
- the GPU has to draw (and copy) a lot more pixels per frame using Xrandr scaling.
If you can’t afford the extra CPU/GPU/power usage then you should try using Wayland sessions instead (where I think fractional scaling is more efficient), or just avoid fractional scaling for now.