The chest are very mean, especially when you need the last 60 stones 
Currently i’m not buying any gear in the arena, i’m getting the stones I need there.
I’ve been spending gems to get all rewards from the step chests. You can’t get many from the shop and you have to wait for shop refresh.
@Cactuar Check up on the arena shop for the stones. I think it’s the only place where stones are not sold out after buying one. I usually wait until I see the stone/stones I need & then buy it several times without refreshing the arena shop.
Ok thanks for the tip, I never bought stones from there before 