User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-5110811-20150606161023/@comment-3045936-20150606162549

Could be script error or oversight. But, in season 7 Death stated that Before God created Angel and Man. That signifies that he meant collectively all angels, unless until a later time is directly stated the Leviathans don't predate the Archangels than we hold that they do. Death just might have listed God and the Archangels as the Participants in the war with the darkness. The Leviathans wasn't called as a participant in the war, so it might be death just left them out in that sense.