So, what's the relationship between Wine and Proton? Is Proton just the SteamOS/Valve name for it, or is it actually it's own project?
It's a distribution of Wine with some extra stuff added, importantly DXVK (directx => vulkan layer) and a lot of game specific workarounds.
More or less Wine + some experimental patches not yet I twgrated in mainstream wine + a buch of DirectX translation libraries + close steam integration.