User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-2602:306:CD9A:C860:A9B0:D607:7141:9234-20190706015400/@comment-28884330-20190706031241

While Vali is slightly superior in specs, they're still comparable as they are both Heavenly Dragon-class. Thus, Issei would have the advantage due to having two Dragon Slayers.