User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170321042248/@comment-31137559-20170322125053

You can be promoted to high-class devil and stay solely as a servant and not receive any evil pieces. It's not like that's mandatory. That is the main privilege of getting promoted to high-class devil but there are those that don't want a peerage. For example, we have high-class pureblood devils that rather be servants than be the king of their own peerage. Why should it be any different for devils that get promoted to high-class?

And it stated on Grayfia's page that she is Ultimate-class. It would be stupid if she wasn't. The strongest Queen, fought in the civil war, has Satan-class powers, and is a pureblood high-class devil. Like she wouldn't be Ultimate-class. The four Satans are Satan-class. Satan is a position AND rank. I don't remember Mephisto Pheles being an Ultimate-class devil. When did it ever state that?

All the members of the Rookies Four showed great accomplishments during the Evil Dragon campaign as part of DxD. Just because they didn't take down any big names like Issei did doesn't mean they don't deserve promotions. We have seen their power. Rias and the others are overwhelming Ultimate-class devils now. Is that enough for you?