Before saying the Marvel Gods stomp. let's pick some information from other Blizzard games and Comics.
According to the LORE, Tyrael is able to travel in FTL speeds and destroys the world a thousand times with ease. But he doesn't because he's just a mere observer.
In Warcraft 3 you fight the Butcher and to defeat it you need a whole army. Yeah, the same butcher you defeat alone in Diablo 3 at level 15 and at Diablo 1 at level 20. The most powerful being in Warcraft is Sargeras. Wich is an eternal god and leader of an universal legion of demons know as Burning legion. He's immune to physical attacks and almost immune to magic. Comparing him to other god it would like comparing us to flye's. So he's basically on the level of cosmic beings from Marvel. If the Butcher was that powerful, we can easily assume the prime Evil is much more powerful than Sargeras or just as powerful.
Now on topic:
The Prime Evil wants to become Tathamet in Marvel Universe. To do that he needs to get to Earth and consume the Hearth of Anu. By doing that he'll become Ethernal, Omnipresent, Omniponent, Omniscient and all powerfull.
All the demons and angels in Diablo universe are basically blood cells of these ultimate beings.
The Prime Evil
The Prime Evil is the main antagonist of Diablo 3 and the most powerful begin to have ever existed in the three universes after Tathamet and Anu. The ultimate omniponent beings of Diablo universe. The Prime Evil is the junction of all Lord of Hells in a single one controlled by Diablo his goal is to revive Tathamet by consuming the Hearth of Anu. The object that created all angels and their plane. He defeats with ease the most powerful Archangel and breaks the Diamond Gates which were said to be indestructible just with his breath. Then goes on a killing rampage for the Hearth of Anu.
By being the Prime Evil he's the incarnation of Fear, Destruction, Hatred, Lies, Sins, Pain, Anguish, Despair and other powers such as Thief of Hope and Banisher of Light all granted by other lord demons.
He's able to use all the weakness against anyone. For example, he can easily turn Hulk against his friends for begin the Lord of Lies and use the deepest of super heroes secrets against them. Not forgetting his powers of destruction.
The Prime Evil can also summon waves and waves of the most powerful demons of hell by opening gates. And he will against Marvel.