Well I have a few ideas. For Envy, the drawback is that it must be returned after a certain amount of time of use and can't be called upon again for awhile. For greed, the object last as long as the user needs it for, but once the purpose of having it is completed, it disappears permanently. Basically, for envy it has a limited time span before returning, and then a cooldown before that specific object can be used again. For greed, it can last as long as it's needed, but once the need is gone, the object disappears forever. Hell maybe for this role we should have siblings using these powers so that way it makes sense that they're so similar. Unless someone can think of a better power for either sin and using the new power for that sin, and this power for the other.