User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-76.95.86.12-20120519182004/@comment-3481504-20120519232017

N, no, no. Way I see it, Cas, while wielding all the souls of Purgatory was indeed stronger than Gabriel and Raphael, however he was adamant on keeping Lucifer's cage, in fear of Michael and Lucifer, as he told Crowley

Yes, the angelic blade didn't work on him, and he clearly said "I'm not an angel anymore, but that wasn't an Archangel's blade.

Also, your comment relates to nothing of Leviathans being stronger than Archangels....Archangels are stronger than Leviathans.