did you know Metal is older than Vulkan by 2 years?

Did you know that Vulkan started out as Mantle which predated Metal by half a year? Anyways, the time of release doesn't really matter. What matters is whether its a graphics standard. Instead of adopting standards and creating a better developer experience for everybody, Apple chooses to go their own way...again. That's the reinvention I am referring to and it causes a trickle down effect that affects everybody else. It's extra work on Apple developers and game devs alike.

Plus it allows them to give complete low level support of their own silicon and hardware that you're likely to not yet with other APIs.

No reason why they can't be done via Vulkan extensions IMHO. Also, I am okay with them having Metal for such purposes...as long as they also support Vulkan and other standards. The problem is that they don't.

A lot of developers also use MolktonVK to get around that support.

MoltenVK is just another example of the extra work that everybody else has to do to support Apple's platform.