Maybe I'm biased as I was involved with the standardization - but the whole point of a standard is something is legally possible to implement, communicates the needed information to the layer below, and general enough that it doesn't require specific hardware.
All boxes are checked by Vulkan? At least that was the intention.
So what if the origin of Vulkan was AMD's donation of Mantle, and the committee knocked the "hardware specific" points off - isn't that the desired result?
Is DirectX a standard? Is Playstation NDK (or whatever it's called) a standard?
Vulkan is not a "standard". It's a designed-by-committee API that arrived on the scene years after "non-standard" APIs.