I think some of the main advantages of the 1D X come from the greater ability to customize the settings. Min shutter of 1/500 s or faster, max aperture, etc.
Compared to a gripped 5DIII, the 1D X is more stable on a tripod.
Of course 1DX has better face recognition when using all 61 AF points.
The 5DIII has no face recognition for phase AF, the 1D X does. So...better? Well, I suppose so...in that having a feature is better than not having a feature. It does come in handy in some scenarios.