Tbf, this mainly seems to compare shitty/outdated 3rd-party Windows drivers against a vertically integrated system where Valve has complete control over both the hardware and software.
E.g. the difference between the Lenovo and Asus Win11 drivers is sometimes bigger than the difference of the faster Windows driver to Linux.
It's also not all that surprising though, there's a lot of very smart people working on Proton while the general quality level in the Windows ecosystem is slowly but steadily declining.
I also wouldn't be all that surprised if running a D3D11 or D3D12 game on a Proton-layer on Windows would be faster than running that same game without Proton. Sometimes Proton might have workarounds for 'API abuse' problems of specific games which the native D3D implementation or driver doesn't have.
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