The difractograms not show a variation of the intensity of the peaks, but the melting enthalphy obtained by DSC is changing with the AM grafted into PP.
In my opinion the x-ray diffraction pattern shows almost the structure of the crystals and is minor sensitive to the degree of crystallinnity, whereas the Thermogramm is sensitive to the degree of crystallinity and the size of the crystallites (resulting in some melting point depression).
With other words I do not believe, that you can compare the two sets of measurements directly with one another, to see possible differences with both methods equally.