It would be great if it would be increased.
But there is one catch. From what i remember standard discount is working only work with 150 and 450 green rolls, while it is not working with 10x hero hiring. One guaranteed legendary for 1200, not 1500 gems. You may use many more gems with 450 rolls and not find single legend.
But suggestion it's is good, 30-40% maybe would be great.