User blog comment:Xilinoc/Ch. 588 - The Headless Star 7/@comment-24384892-20140709124531/@comment-1268838-20140711052120

The thing to keep in mind is that the act of giving the Sternritter a part of his soul isn't what gives them their unique powers. He has to engrave the Schrift on their souls with it. And I highly doubt that Yhwach has the entire alphabet inscribed on his soul, especially since he specifically designated himself as A.