To add to that, I thought one of the key benfinits to DX12 was lower level access. Don't both the Xbox One and PS4 already benifit from that?
He was talking about GPU being fed by CPU. Basically he just said that if You are GPU limited DX 12 wont make much of a difference, which is true and already seen not only in DX11, but also in Mantle.
But generally thats not that accurate in the long run of any lower level API. DX12 gives much more control over rendering pipeline, which can enable new techniques [async compute is one example, using msaa hardware for other stuff is other].
Also it helps with CPU parallelization limitations, which maybe wont help now, because we are GPU limited, but can help in future, especially for VR that requires high framerate and CPU bottleneck in DX11 could limit that, even on lower settings.