Obviously the xp gain/requirementa need tweaked, but after my 3rd rewars reset and still not seeing any legendaries. (Currently have 13 legendary equipment dont care for epic or less)
So just do modify the rewards from rolls.
D6 gives gold
D12 gives 50% common 50% rare.
D20 gives 20% legendary, 50% epic, 20% rare, 10% common