If they nerf spell cost reduction to 7% per stage this will be lets say 30% ultimate reduction + 20% from set + 15% as sorcerer + 5% as emperor which reduces the cost from 200 to 60 ultimate but you can further reduce it to 45 with another set.

I'm sure certain sorcerers will still be able to spam their ultimate because you even get 25 ultimate whenever you kill someone.

I would suggest to buff the decreased spell cost to 40-50% but it shouldn't apply to the ultimate.