User blog comment:B214/Volume 22 spoilers/@comment-95.90.227.198-20170201191840/@comment-201.214.186.100-20170202012441

even if Issei surpasses Vali, Vali will surpass him again, and he does, then Issei will once again surpass him, because that's just the nature of the heavenly dragons, the reason why Ddraig and Albion became the strongest was because they were never contempt with just one surpassing the other once, their strenght just kept growing in their relentless competitons.

The reason why Issei and Vali are abnormal is because they're following the same train of thought that Ddraig and Albion had, and are working hard to master their powers to perfection, in other words, they're skillfully swimming in power, and not just diving and drowning on it like the previous possessors