And, at least for the early version for Proton, out-of-the-box controller support. You simply do not want to mess around with this manually on wine.
Yes, Vulkan is awesome, but its biggest benefit apart for performance is DX11+ support.
Wine had DX9/10 for ages now, and many Proton games don't depend on Vulkan to run.
D3D10 and D3D11 are very similar (I remember DXVK claiming that, which is why the supported both at once).
I don't think we had usable D3D10 support before DXVK, but I may be wrong.