Idea: Exhaust penalizes Zed's ultimate damage through mitigation

Currently, Zed's ultimate will calculate all damage dealt to a target pre-migitation. That is, if Zed deals 1,000 damage (but is penalized to say, against 50% armor), his ultimate will calculate off 1,000 damage.

However, if Zed is exhausted, his ultimate will still calculate off his base damage, even though he is penalized by 40% of his dealt damage. So even though he does 600 damage (original 1,000), it will calculate off the 1,000 damage.

This massively hampers the effectiveness of exhaust against him as a defense spell, as well as any other source of -DMG (e.g, Sona's passive). Perhaps we could make it so -DMG modifiers properly reduce his ultimate's damage (excluding armor sources)?