This is an area of active development that will continue to see improvement.
At these pixel sizes (except 125%), it is irrelevant. MacOS and iPhone do exactly the same for years, and nobody was ever bothered.
> along with the performance overhead.
By the increased resolution of the framebuffer; the scaling itself is done by hardware (and here I do not mean GPU; I mean output encoder).
Oh, it does. The framebuffer is integer scaled, but the physical display has different (lower) resolution. As I wrote above, this mismatch is handled by the output encoder.
> Macs are all designed to run at 200%, though you can set it to 175% or 150%.
Macs since around 2016 ship with ~175% default.
Again, the framebuffer is integer scaled (make a screenshot and see for yourself), and then fit to the display with lower resolution.
They do not support 150% or 175% though; these numbers are never shown in UI, just some description like "more space". This is not just Apple-esque hiding of everything that might sound technical; they really do not support 150% or 175%. In reality, it is more like 177,78% or 152,38%; they get something out of it, but that is a different topic.
It is exactly the same approach that Gnome / Mutter uses for fractional scaling. Except that Mutter did the mistake with exact scales.