I posted a comment about this in a thread I had made about something else, but then I realized I wouldn't get as many replies as I'd like.

Regarding the battle with Jyggalag, I wonder about the implications of a mortal fighting against a Daedric Prince directly like that. Deities in general are untouchable in TES. A mortal cannot defeat one of them in single combat, no matter how strong he is.

That's why the best you could do in the Dragonborn questline was defeating the pawn Miraak, as Hermaeus Mora himself is beyond your reach regardless of your unique powers.

Sure, there is the final battle with Hircine in the bloodmoon DLC, but you don't really face his full power, just a portion of it.

And just to avoid making too many threads, I'd like to add a second question. Considering that Mehrunes Dagon was defeated by a mere fraction of Akatosh's original power (before Creation), aren't Aedra actually far superior to the Daedra?

Depends on your point of view, really. Some people belive that the Daedra are the true Gods, because of certain "gifts" they have. One being, they do not die, rather reborn in Oblivion. Two, that when they choose they actually converse with mortals and appear, rather than being silent. These were just some of the points from Mankar Camoran.

The Dragonborn was in Hermaeus Mora's realm. That's where Mora is completely in control. If he were to face Mora in Tamriel - if that's even possible with the events of Oblivion; however Sanguine appeared in Skyrim...- he'd maybe have a chance of banishing him to the Waters of Oblivion, however I doubt it.

As for that aspect of Akatosh defeating Mehrunes Dagon... Akatosh is the chief deity. He's the one who came before all others. He's the Time Dragon. He's the strongest of the Aedra. That's probably why he was able to defeat Mehrunes Dagon on Nirn; but in Mehrunes' realm? No way!