User blog comment:Madman97/The Aedra Vs. The Daedra theory/@comment-3025184-20131010203442/@comment-3025184-20131012052850

Also, the reason Alduin was weak was because he abandoned his role as World Eater, hence losing the vast majority of his power. Many people complain that Alduin was too small to be a world eater. Well, if he was in his true form, Nirn would have been devoured and the Kalpas reset.