I am a grandmaster diviner and i did so many quests for so much exp and nothing to do with it. i had an idea when the level caps raise that all those exp points can be shifted to he present level like if you earned 10,000 exp before caps was raised you can add those to you level.
After level 50, no new experience is rewarded. Experience you would have received from quests or duels that you complete after you reach level 50 is lost forever.