I believe you're correct, because they know the exact hardware they don't need to be compiled for each device unlike how PCs come on every version imaginable.

I have definitely seen my deck compile shaders, however I assume it downloads them if they are available. If you launch a game that uses proton for the first time while offline, you should see it compile.

You can disable that feature, and some people do because they get tired of the constant downloads and shaders taking up space for games they haven't even played yet.

I'm running a 6700XT and weirdly enough it pre-compiled in Linux but not in Windows.

It's really stuttery for a while in Windows, with low GPU usage and erratic frequency, until it normalizes.

I'm getting none of that in Linux, smooth from the start in-game. Only getting some weird fps fluctuation in the start menu.

CS2 compiles shaders on my desktop. It does so every time it updates. Also, why would this make the game worse on AMD? Afaik RADV supports VK_EXT_graphics_pipeline_library, just like Nvidia. Shader compilation performance should be similar between them.