To create an interesting experience you need variety in that experience.
Epicness is relative to the expectations of the player. If all your quests are epic, none are.
As mentioned, the focus needs to be on quality of quests.
How epic they feel, is just a knob to increase the perceived quality of experience without actually changing the complexity of the content (youre just using bigger numbers and words and so on).
So you can slowly increase the epicness factor, but occasionally you need to recalibrate the players expectations so it doesnt get too crazy. I would accompany this recalibration with particularly interesting content (because obviously going from "epic" to "mundane" is not very fun, so you need to compensate). Like maybe you complete the epic quest and go back to boring life. But from that quest you got some interesting items or skills or knowledge, that keeps you interested enough to tolerate the lowered amount of stimulation for a while (epicness is just one factor of quality of experience, so you are simply switching from relying on rising epicness as a source of quality, to some other factor like new content - overall quality of experience should thus stay constant).
Consider the storytellers of rimworld. They determine how events that happen to you in the game are 'scheduled'. Rising challenge (~epicness), steady, or random.
The existence of options here means that players have different preferences. So maybe you can add an explicit option, or allow players to affect this through gameplay choices.
Maybe some players choose to go on a journey of increasing epicness, while others occasionally go on an epic quest and then return to normal life. And others get themselves in a situation where epic quests are forced on them without much control.