User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-39.33.129.244-20180502100635/@comment-28884330-20180502182748

Crom is still weak to dragon slayers, and Issei has not one, but two of them now on top of Penetrate. So even if Vali 's DxD L and Crom are slightly more powerful than Issei's DxD G, Issei has actually a better chance of defeating Crom than Vali did, and this chance is nothing to sneeze at, seeing as how those same Dragon Slayers are what allowed Issei to defeat a Vidar who had surpassed Thor in raw power.