The issue is not that we are worried about them ditching OpenGL. If they did that then they would lose a significant portion of their developer base, destroy what little gaming market they have, and result lots of major cross-platform software breaking. If they were to ditch OpenGL, they’d have to open up the specifications for Metal or risk a collapse.
The issue is that developers who use Metal will be given an unfair advantage over non-Metal, resulting in people switching to Metal, and therefore resulting in lots of non-portable software.
And I would go as far to say that I would be surprised if Apple didn’t give Metal developers an unfair advantage.
Luckily, the majority people who develop software are aware of Apple’s bull****, and so the only people who are going to fall for it are the Apple fanboy developers.
So, not that much of a problem, unless you heavily use Apple devices.