Re: APIs
It's a detriment to the developer, because Metal only exists on Apple devices.
So anything they do on the Metal they cannot use on anything else, raising yet more walls around the garden.
This is why there are projects such as MoltenVK and a host of shader translation tools, to allow GPU work to be ported onto Metal.
He might have had a valid point if Apple had instead put their effort behind a cross-platform API, but instead it's yet another brick in the wall.