Here is how to rebalance Azir without actually nerfing him.
Cut the damage on his Q by half, give his soldiers an additional 75 range on their auto attacks and bring up the 25% from additional soldiers up 10% and congrats you now have your sustained dps mage like everyone wants while keeping him relevant.
No more will you be chunked down from his Q spam, but instead punished for standing in his soldiers area of influence.
He wouldn't be bursting you down whenever you set foot near his area, but instead wittle you down depending on how much time you spend in his soldier's attack range.