Didn't Vulkan omit a way to query for active displays so you just have to pick a random display index when your application starts up?
Other than that I thought Vulkan was pretty decently comparable to Metal. I don't have any first hand experience with it though.
That sounds more as if it would be a window system specific issue? As far as I know OpenGL didn't have that kind of API either and you had to use X11 and the glX bindings for that kind of information.
Mediocre on Linux? Since when?