Catalyst doesn't exist anymore, it was replaced by AMDGPU-PRO years ago.
The Radeon Mesa driver (radeonsi) is generally faster than AMDGPU-PRO OpenGL for gaming, and has been for years. On the Vulkan side, performance is usually fairly close between the Mesa driver (RADV), AMDVLK and AMDGPU-PRO.
AMDGPU is just the kernel driver, which is used by both the Mesa drivers and AMDGPU-PRO, so why is it listed separately?
For Intel, I think the hardware was holding it back more than the driver, especially since they've replaced the classic Mesa drivers with Gallium based ones. But now they're doing the Arc stuff.
I don't know if I would say that Nvidia proprietary runs well
Which will be duplicated for everything installed application, and redownloaded for every new version. Whereas flatpak and snappy shares the dependencies between applications.
Without the recently added wp-fractional-scale-v1, yes, it will do that if you use fractional scales (albeit per window rather than per monitor). Not however if you stick to integer scales, as they might do in the 1080p+4k use case.
It's worked just fine for the past century