User blog comment:B214/Volume 23 discussion blog/@comment-77.188.219.183-20170424022727/@comment-29963364-20170424130102

There's another reason why there is a power difference between Issei and Vali in their EJOD and CCP armors respectively.

It's because Vali has more power than Issei in their base forms (without using their SGs).

So even if the EJOD and CCP were exactly equal in power (CCP will be equal when Issei completely masters it), Vali will still have an advantage in power.


 * Vali: Base + EJOD = Ultimate/Satan-Class Devil + Heavenly Dragon-Class


 * Issei: Base + CCP = Mid/High-Class Devil + Heavely Dragon-Class

Do you see the difference? However, this only applied before vol.12. Issei now has a Dragon Body made from Great Red's flesh and possesses Ophis' power. So the difference in their Base Power is practically gone (Issei might have the advantage when he awakens his body's power).