User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-2602:306:CD9A:C860:A9B0:D607:7141:9234-20190706015400/@comment-2607:FB90:27A:5FC3:0:0:9FA6:3B01-20190706120425

Issei has more destructive power, dragon slayer and penetrate hax going for him, he's also a semi-experienced fighter at this point. Vali basically outclasses him in everything else, technique, magic, versatility and speed too. He also has many years more fighting experience than Issei. Issei's greatest strength is his unpredictability but that's not reliable enough to pull out a guaranteed win. At the end of the day, Vali still outclasses him, but Issei definitely has a chance with his hax powers and random asspulls.

I made a mistake when I said stamina so let me phrase it better. Issei cannot use his strongest attacks multiple times. Infinity Blaster and Compression Divider are one of their strongest attacks but the difference is once Issei uses Infinity Blaster, he becomes exhuasted and cannot use it again while Vali could use his strongest attack and have more than enough power to keep going. This was shown in his fight against Azi and Crom. This is likely due to the difference in demonic power quantity.

Also Vali has shown he can more than just offensive base magic. In volume 4, he was able to seal Gasper's eyes to prevent him from using time stop so we know Vali has sealing magic. Now while dragon slayers are a threat to Vali, it would be very difficult for Issei to hit him because Vali outclasses him in speed which means he can easily dodge them.

Final result: Vali wins in a 1 v 1 7 out of 10 times He is more likely to win than to lose, but with issei you just never know