Earlier quoted context omitted.
Yes but there's nothing surprising about the Walled Garden Company promoting their own snowflake version of Vulkan and insisting everyone who wants to run software must do things their way. This is the same company who has totally locked down the tooling to create and publish iOS apps to only be possible on their hardware.
To be fair, Metal is more than a "snowflake version of Vulkan". For one thing, it was in production before vulkan, largely to address the issue of OpenGL's overhead on mobile devices, and basically it achieves that goal. Also there are certain things which are exposed in Metal which are not in Vulkan, for instance more control over the tile memory which mobile GPUs use. So it's not as if there is no reason for Metal…
An advantage of all proprietary 3D APIs is the amount of out-of-box infrastructure code, debugging tools and having progressed beyond C, while Khronos APIs are still mostly C, and requiring creating mini-engine from scratch after fishing for libs.