User blog comment:Jett Cyber/Tournament of Legends: Round 1/@comment-9062114-20131024005007/@comment-13446185-20131026155135

I was basing my answer off of the fact that Alduin is not longer stronger than Mehrunes. Alduin being an aspect of Akatosh was bound to Mundus just as Akatosh was. Obviously before this (When the Leaper Demon King existed) Alduin would be able to destroy Mehrunes, but now Alduin has lost an extreme amount of his power.