User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-76.95.86.12-20120519182004/@comment-5110811-20120521174842

It took longer to plot because there were careful steps to be taken. His opening of his cage is far more complex than opening up purgatory. I don't know why you don't get this. His cage is the 9th level of hell where even if you open hell up, Lucifer is still stuck in his cage. When Purgatory was opened, Castiel absorbed everything the monster souls and the Leviathans.

And there is a clear delineation between Archangels and angels. Archangels have shown to overpower anything except God and Death. They have shown to be a true anomaly being able to overpower all pagan gods, angels, monsters and demons. Michael along with his 3 brothers are closest to God as a son and have actually seen his true image. Because of his purpose and nature of his role as the viceroy of heaven, being God's second in command and power with the exception of Death. It would make no sense for him NOT to contain the Leviathans. It is highly likely that Michael and Lucifer are an anomaly to the Leviathans, even able to override the leviathans immunity. Just like the way Alastair, Azazel, and Lilith is immune to Ruby's knife. The four Archangels are a few elite brand of beings that are immeasurably superior in every way compared to all angels.