User blog comment:Ixarising/High School DxD Dream Battle/@comment-112.211.199.137-20140207162046/@comment-1359322-20140207172258

You forgot the fact that Rias used her oppai beam to support Issei when fighting Cao Cao.

And the Raikoryuu was capable of paralyising even Grendel, a Dragon with perhaps the toughest defence, i don't think Issei at his best could withstand being hit by that. There's also the issue where Issei is weak to light being a Devil.