User blog comment:B214/Volume 23 discussion blog/@comment-185.112.105.215-20170504164928/@comment-30048084-20170504200739

Rias is not yet at the level of an Ultimate-Class Devil, Fighting an Ultimate-Class and being one are two different stories. For all we know the Ultimate-Class Devil she fought was at a disadvantage because of the nature of their abilities or even that the Devil in question was extremely weak in comparison to other Ultimate-Class Devils.

In the question of Ultimate and Satan-Class Devils the difference is incomparable.