Alduin has defeated Mehrunes Dagon twice. Once in the Oblivion Crisis, once in the time of dawn.
Molag Bal, being in Akatosh's position in the prior kalpa, could no doubt be of an equal match to him.

But at any rate: all battles between et'ada are catastrophic. Such encounters are to be avoided at best.


Nope. Dovahkiin was a son of akatosh within the shell of a mortal- big difference. Alduin has also defeated Mehrunes Dagon in the semi-canonised
Micheal Kirkbride (a former developer who worked on Elder Scrolls III: Morrowind) scripture: http://www.imperial-library.info/content/seven-fights-aldudagga. In them, you can
see the origins of the painted cow random encounter within Skyrim and the source for the whale bone bridge in sovngarde, both mentioned there.

Also: contrary to popular belief, Alduin is actually an aspect of Akatosh- which is why you could not absorb (thus destroying) his soul at the end of
Skyrim. To annotate this, look at Alduin and Mehrunes Dagon's death animations in both games. See the similarities? well, go figure on why's that.

As well: Dovahkiin belongs to the oversoul known as Talos. They're a shezzarrine, as the greybeards rightly point out upon first meeting them.
Do not know the reference? they call you Ysmir and note upon Stormcrown's last visit to them. As well, Shor's throne in Sovngarde is quite empty.

This I hate it when people say Alduin died to a mere mortal when in fact he did NOT he died to someone with so many ties to the gods he is a demi-god himself.