Simple thing, not a huge game changer. But how about if you complete a dungeon with a max level champ, or more than one for that matter that the wasted xp that cant be credited to the champ could be rewarded as silver? If 100% is too much then maybe 50%. But keep in mind that running 12-3 brutal is around 9250 xp, that would be 9250 for running with a max level champ, not that much but something.