Mantle is necessary. DX11+ is all about MS and their desire/attempt to control "all things compute". OpenGL failed because it didn't have the necessary backing and business compunction to succeed in the face of a virtual monopoly the likes of MS.
AMD will probably succeed because they have far more compunction, far more to lose if it fails, and MS is far weaker now than before due to the software competition provided by Google (Android) and Apple (iOS) and the app environment created in their wake.
AMD will probably succeed because they have far more compunction, far more to lose if it fails, and MS is far weaker now than before due to the software competition provided by Google (Android) and Apple (iOS) and the app environment created in their wake.