Having an ability to craft custom items that are only available to you would give numerous advantage over other players who don't have that recipe unlocked (That's the closest thing I could come up with since I am not sure what you're actually referring to by 'crafts/recipes').
Even though these 'custom recipes' would be purchasable through gems as you're saying, it really depends on what they would be like in the end. Since there are no kits in the actual game, it means that everyone is equal to each other and the real key at winning the game is planning your strategies two steps ahead, and not relying on your kit's ability. What I like about UHC is how everyone has the same chance at winning it.
