No, I just have a hard time believing there are 20 million XPs in epic content without repeating some quests a lot.
There are 103 total epic quests & raids. You would have to average 192K XP per quest to be able to one and done all of them and get the 19.8 million XP you'd need to go from 20-28 three times. Add in challenges, that's another, what, 8 or 10? That still means each quest/challenge/raid would need to average 175K XPs per quest. Is that what you are averaging?