User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170321042248/@comment-141.135.80.110-20170321051113

Rias didn't overwhelm an ultimate class devil by herself she tag teamed one with Akeno by her side. It's been stated several times class isn't awarded just for beating X otherwise Issei would be a Super devil by now. They were rewarded for extraordinary service for the Underworld. The old devils don't want it but the common devils want them to get promoted. So they cut a deal with just promoting Issei,Akeno and Kiba they'll get there in time they have ten thousand years to live it doesn't really matter.