You can't adopt stuff which doesn't exist.
Apple was the first to release next-gen 3D API, Metal was released in 2014. Then came MS, DX12 was launched with Win10 in 2015. Vulkan was too late, initial release in 2016.
Apple was the first to release next-gen 3D API, Metal was released in 2014. Then came MS, DX12 was launched with Win10 in 2015. Vulkan was too late, initial release in 2016.
It was done exactly for the Apple to be "first". The initial Vulkan release was more comprehensive than Metal 2 in 2017.
Nowhere was mentioned, that Metal 1 and Vulkan 1 were not comparable by a long shot. Exacly, precisely because it was MVP focusing on specific mobile GPU.
So. What about Mantle?
(Note: I in no way imply that you spread false narrative etc. It just happens that this linked comment is such a reply)