User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-79.103.157.220-20151213224431/@comment-26982641-20151213230436

Even in Limbo, Lucy could erase them. Also I think Darkness could destroy them or negate them without effort but they were under God's wing just as Crowley was under Raphael's wings. So Cas couldn't smite him.