Balanced Counterspell

You attempt to interrupt a creature in the process of casting a spell. If the creature has cast at least a level 1 spell, it makes a Constitution saving throw (if the creature has cast a cantrip it automatically fails the saving throw). On a failed save, the spell dissipates with no effect, and the action, Bonus Action, or Reaction used to cast it is wasted, but the slot isn’t expended. The DC of the saving throw decreases by a number equal to the difference between the slot level of the spell that was being blocked and the spell slot uset to cast Counterspell; the DC doesn't increase if the countered spell uses a level 1 or 2 slot. For example if the creature has cast a level 4 spell and you decide to cast counterspell using a 4th level slot, the DC of the saving throw is still equal to your DC; if the spell was cast using a 7th level slot and you use your 4th level slot to counterspell it, the DC of the Constitution saving throw the creature must make decreases by 3.