User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-86.159.50.151-20120508103555/@comment-98.113.182.208-20120508164728

keep in mind there are hundreds, thousands, tens of thousands, maybe hundreds of thousands of leviathans inside God Cass trying to gain control over his vessel. So them breaking God Cass apart bit by bit doesn't really say much about thier power since it's the entire species in him battling for control.

Since God Cas is equal to Michael and Lucifer given how wary he is to have them both in the cage at all times by letting Crowley to live to make sure of that. I'd say a single leviathan would be no match to an archangel.