User blog comment:B214/Question and Answers 6/@comment-190.164.227.239-20161201033222/@comment-10330822-20161204142837

Well his stamina has to be ridiculous because he maintains Scale Mail and CCP like he is Vali. Same with DxD G, just like Vali. I think he's stronger than people think, because if he is the weakest, those previous possessors much have been stupidly strong to be that much stronger than him. Still, he's a devil and a dragon, much means his body is naturally better than that of a human, which is normally what is using Boosted Gear. If Issei isn't already stronger than them, you should be able to be so given enough time. After all, he seems like he might be the first Red Dragon Emperor to live past 200 years since he is a devil.