User blog comment:Piyush Banerjee/Shin DxD 2 discussion/@comment-2602:306:CD9A:C860:A9B0:D607:7141:9234-20190706015400/@comment-2602:306:CD9A:C860:A9B0:D607:7141:9234-20190706092258

Having Dragon slayers does help Issei but he would ultimately lose to Vali. Vali has too many specs in advantage. Due to having higher demonic power and stamina, Vali can easily outlast Issei. Furthermore, while Issei has dragon slayers, Vali can use magic as a way to counter that.