But that is the fault of that 3rd Party software developer. Neither Blizzard, Apple, or Microsoft can control the updates from a 3rd party. DirectX12 is not new.
And if you’re running a “Hackintosh”, which is not supported by Apple, then your solution would be to not use OS X and boot to Windows 10.
As for gaming performance under OS X, there are plenty of articles, like this one that point to Apple not giving a poop about gaming. Keep in mind that when Patch 7.3.5 hit, Blizzard sent warnings along with it that Mac Users, and PC Users not using Windows 7/10 and having a DX11/12 card, we being cut off.
And you say Metal supports EFS, but what about Metal 2? And can Metal do it without having to use OpenGL? Because one thing to remember, Apple deprecated OpenGL completely and officially not too long after 8.0 was released. And chanced are Blizzard knew that change was coming. I kept looking but Metal is not nearly as well documented as DX is.
And this isn’t the first time Apple has pulled this crap. Adobe users on the Mac side were furious when Windows got the first 64bit version of Photoshop and Mac did not… all because Apple at the last minute decided that Carbon was not going to get 64bit support and tried to force everyone onto Cocoa. And Adobe was not going to delay release just for that.