They are not behind their windows driver on OpenGL. And neither for Vulkan, I think. AMDVLK scores a few wins here and there, but RADV is generally more stable, performant, and compatible. Plus being open-source, it is easily extended, like valve is doing with their AC0 experiment [1].
Last I heard, people were installing Linux to use the AMD OpenGL drivers to play emulators (it might have been Cemu, actually ran trough wine).