User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-2001:E68:6DD9:1200:D458:2702:1DBF:38D9-20180102061813/@comment-29963364-20180103032313

Great Red isn't counted amongst the Top 10, because he "isn't a combatant." Meaning that even though he is unanimously regarded as the "strongest in existance," he doesn't participate, or show any interest in the affairs of the world. So they don't bother counting him.

The reason Ophis is counted, despite being on par with Great Red, is because she actually does interact with the world. Azazel even said that he's seen her roaming the world (in the form of an old man at the time).