User blog comment:B214/Question and Answers 6/@comment-24098614-20170326152005/@comment-10330822-20170327033145

Well, to be fair, Vali trained to beat Rizevim after Volume 16, so it always hasn't been about just getting stronger. Granted, he's insentive for beating Rizevim is completely from Issei's.

I know Issei has a sort of "power, juggernaut" thing going, and I understand the author not changing it, but at the same time, the magic could make a lot of his other abilities much smoother. Take Rossweisse for example, the raw strength she has in magic, coupled with her Rook piece, makes her that much stronger. Showing that when you are insanely strong, your magic can be that much stronger.

Also, I feel it limits Issei's character in a way, when you are nothing but raw strength, what do you do when that is enough. So far, Issei has just been growing even strong and overcoming these issues, but you have to imagine he can't just bulldose characters like Typhon and Indra with raw power alone.