The game is sorely lacking in gil sinks, so I don't mind the more exclusive rewards in Eureka being locked being RNG. If someone really wants a particular item they can either brave the grind and try their luck...or just buy it outright from the market board. At an inflated price, granted, though even at a casual pace gil isn't too hard to make in this game. I do agree that the game should stop leaning so heavily on materia as a reward, though. It practically throws it players these days so selling it on the market board often isn't wise and leaning on transmutation is just another layer of RNG and one that can be rather tedious and time consuming to engage in.