Vulkan is that it's a much more modern API

Absolutely, older APIs tried to smooth development by abstracting more from the hardware, Vulkan tries to give the developer as much control as possible. If you know what you're doing you can write more performant games with Vulkan, but on the flip side development is slower. The matters less and less though, as most game dev these days uses middleware like Unity or Unreal which does all the graphics pipeline management for you. This also ties into modern graphics hardware being more configurable than ever, meaning the more restrictive APIs can waste a lot of the hardware's potential.

I did a bit of research after reading your comment and from what I can see, Elden Ring has some bugs in it's rendering pipeline that can cause cached shaders to be recompiled for no reason, this is what causes all the stuttering on Windows. Proton devs managed to write custom implementations of the DirectX functions that it uses incorrectly, to force it to work the way it was presumably intended to. That's awesome to me and really shows off the potential of Proton. Obviously other games which aren't huge releases aren't going to get that kind of treatment, but I can definitely see dedicated communities fixing issues like this in games.

Super cool, I'm glad you mentioned Elden Ring because I hadn't considered Wine/Proton could be used like that.