User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-5.13.171.192-20180430092626/@comment-26285797-20180501160346

If he can beat Typhon in pseudo DxD G, they very well maybe on par with one another, but that's without any of the details of the battle. As for now, I'd say Vali's is marginally stronger, but that may be because Vali's talent as a fighter and as a dragon is greater than Issei's. Since the LN seems to be hinting that Issei may end up gaining Dragon God level strength, I wonder how Ishibumi will give Vali a power-up to ensure that he is able to continue to compete because Vali is Issei's true rival.