User blog comment:B214/Volume 21 info & spoilers/@comment-26345952-20160711012832/@comment-26709288-20160711062127

Diehauser doesn't really need his ranking raised considering he's already a ultimage class devil and #1 of the Rating Games, that's like adding more water to a already filled cup.

But to answer the initial question, in my opinion Issei with penetrate amd Diehauser with worthless are a pretty even match. I feel their fight could go either way.