User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-77.192.107.58-20190929160022/@comment-77.192.107.58-20190929174741

He didn't say that CxC was the problem for P DxD, he simply said that with better mastery of CxC, Issei would master better P DxD G, what is logical considering that DxD G is CxC plus Ophis' power.