That’s a wild exaggeration. Yes they underperform relative to the Windows drivers but my experience is far from “cutting framerates in half” nor “borderline impractical”. I’ve had the last four generations of Nvidia card (currently on 5070Ti) on Linux and played demanding games just fine.

This is not true at all. I game on Linux (Arch, btw) on my 3090 and every game not using some kind of kernel-level anticheat just works. I have never made formal comparisons, but my experience is that I can't notice a difference in performance relative to Windows most of the time. One exception was Helldivers 2, but the performance gap has more or less closed recently with recent Proton versions.

The only problem with Nvidia in the last... 5 years was their wayland support and their worse than expected performance for DX12 games. Both of which were being actively worked on, where wayland support has been improving since 2 years ago and DX12 performance needs patches on all the stack, the driver is there, mesa and vkd3d patch are pending.