RNG should never be used to take from a player and completely negate time/effort/money. It should only be used for boosts of some kind. Take the light grinds; they'd operate as normal, but by a low % you'd have a chance to get a double-potency light gain. Or for the dungeon drops, each completion should go towards a token of some sort that can be used to acquire the thing after 10 runs or what have you, but there's also the small chance you get the end result and it discards the tokens.