I have seen nothing to suggest that Archimonde is stronger in lore than Deathwing. Aspects and Elemental Lords have always been shown to be second in power to Old Gods and Titans. And considering I doubt we ever face Sargeras directly, or an Old God that is actually awake and free, Deathwing will likely remain the most powerful villain we face. I put him over Ragnaros just due to him being both an Aspect and having Old God corruption.