Thanks for that,
I did only have desktop gl enabled, not gles, but does this therefore imply there is no 'native' OpenGL backend on windows that takes advantage of opengl4.2 etc, ie: there is only the OpenGLES backend which goes through angle?
Here's the thing: there is a desktop GL backend in Dawn, but there is currently no WGL support, which would be necessary to access it "natively" on Windows (we used to do it through GLFW but that was problematic for various reasons). The correct way to implement it now would be to create a ContextWGL subclass of dawn::native::opengl::Device::Context, as is done with ContextEGL.
Not a problem really, I was mainly just interested in comparing performance/consistency etc, but native d3d12/vulkan vs. angle doesn't sound fair!
I'm in the process of resurrecting my linux build so I'll play around with the GL backend on that instead.
You're likely to have more luck there, as long as your Linux machine has an EGL driver that supports creating desktop GL contexts (most NVidia drivers do, for example).