I think I would nerf baneling health, and also Buff Thor's AA damage. They are so slow and chunky that mutas just kill you.
On the Protoss side... Viper is simply too useful of a unit, and Zerg can Macro too much. That's why Protoss is forced to all-in. This has been true since Wings of Liberty. The inhernt strenghts of zerg are just too wook vs the inherent waeknesses of protoss (Each race has strenght and weaknesses, it's just that the Zerg ones play a little bit to well vs the Protoss).
Honestly, I think they should nerf larva output. It get's completely out of control in the Mid-Lategame.
That or nerf the queen so it's easier to harass zerg so at least you can deal damage and they are forced to re-drone instead os just easily maxing time and time again.