I don't see anything wrong with some sort of buff you can obtain that reduces exp, allow the player to choose the amount too cause why not. Maybe some custom options too, like story mode exp which prevents exp leveling you past the MSQ you have (so like you can't level past 11 unless you finish the level 11 msq, it can store the exp you've earned so far too, just so it gates you, by your choice, at the MSQ level).