Metal is neither a general-purpose compute API or a known example of Apple supporting it. If you consider Metal "general purpose" then so is DirectX or even Playstation and Nintendo shaders simply because you can sum matrices.

Accelerate framework might be what you're looking for here, but by most accounts that hasn't improved very much recently. And even still, Accelerate is no analog for OpenCL or CUDA.

Metal is basically equivalently powerful to CUDA, so I'm not entirely sure what you're getting at here. I mean, it's literally Apple's CUDA but for their own hardware.