As someone who likes the idea of Teamfight Tactics, but hasn't enjoyed a few of the balance changes, I have a little idea to balance some of the more frustrating parts. My first idea: Remake the Phantom debuff to be a 2-4 treat, and make it so that 2 of the class lowers one random enemy champion to half health, and 4 lowers 2 random enemy champions to half health. Add Thresh as well, he could be a Guardian/Phantom, and his ability would be a reversed Blitzcrank hook. He targets the closest enemy, and diverts the aggro of his teammates. This way, you make Phantom a less frustrating treat to fight against, and you add a very tactical champion!
Next, Hextech. You've probably heard complaints about this one. I think Hextech should not be an AoE effect, but should target 1-3 targets based on the amount of hextech champions you have, and always debuff for 7 seconds. This way, players dont have to spread out their comp entirely because a single person has Hextech, but Hextech doesn't lose its power.
I hope you can take this into consideration!