Jagar Tharn can be presumed as an Imperial, Dagoth Ur's attack is really just a touch of god rather than a being a traditional spell caster and Underking isn't really classified as an antagonist in Daggerfall (he doesn't even appearence or sound like the the evil being they made him out to be).
As for the "Epicness" of the Main Quest, we seen enough gods for now. Let go to something a bit different.
As Symmachus had predicted, the theft of the Staff of Chaos had few short term consequences. The current emperor, Uriel Septim, sent some rather stiff messages expressing shock and displeasure at the staff's disappearance and urging that Symmachus make every effort to locate its whereabouts and communicate this to the newly appointed Imperial BattleMage, Jagar Tharn, in whose hands the matter had been placed.
"Tharn!" Symmachus snarled in disgust and frustration, as he paced about the small chamber where Barenziah, now some months pregnant, was sitting serenely, knitting a baby blanket. "Jagar Tharn, indeed. I wouldn't give him directions for crossing the street."
"What have you against this person, husband?"
"I just don't trust that mongrel elf. Part wood elf, part dark elf and part only the gods know what. All the worst qualities of all his combined races. No one knows much about him. Claims he was born in Valenwood, of a wood elf mother. Seems to have been everywhere since--"
Barenziah, sunk in the contentment of pregnancy had only been humoring Symmachus thus far, but this piqued her interest. "Nightingale? Could he have been this Jagar Tharn, disguised?"
"Nay. Human blood seems to be the one missing component in Tharn's ancestry." To Symmachus, Barenziah knew, that was a flaw. Symmachus despised wood elves as lazy thieves and high elves as effete intellectuals, but he admired humans, especially Bretons, for their combination of pragmatism, intelligence and energy.
-The Real Barenziah, Part X
Dagoth Ur is a spellcaster. This guy clearly has a firm grasp of magical practices. Whether his actual attacking style is what you say it is or not does not matter. No warrior or thief could do what this guy does.
Main quest epicness is not really a question of fighting gods as much as it is one of saving the world from power-hungry, long life living sorcerors, from what I'm sensing here.