Vulkan probably wouldn't help macOS gaming from a users' point of view, but it sure would be nice for us engine developers. There aren't many Vulkan games, but the big 3 non-in-house game engines (Unreal, Unity, Godot) are all committed to supporting Vulkan in addition to Metal, so we (collectively, the engine dev community) currently have to support both. Dropping Metal would reduce the amount of engineer time spent chasing down Metal-specific bugs (which is not inconsequential), which allows us to spend more time on actually interesting features that users want.
Metal is a hidden tax that isn't obvious, but it's there.
Metal is a hidden tax that isn't obvious, but it's there.