My changes I'd like to see:
McCree - The current elephant in the room. Maybe less damage when fanning the hammer, considering the usual combo of flash - fan - roll - fan can destroy tanks.
Torbjorn - When Torbjorn dies, his turret should die too, or maybe "deteriorate" since theres nobody to bang it with a hammer.
Bastion - lower Ammo when in turret mode, or longer reload time. Slower turn speed? 100 bullets?
Zenyatta - Could use some more health, can currently get bodyshotted by Widow. At least be able to survive that, hes PLENTY squishy as is. I'd love to play this guy more but he's just TOO squishy for me, even more than a Mercy!
D.Va - OBVIOUS, lower the radius of that ult... holy moly
Symettra - For a "support" character she has no form of healing like all the rest. What? Mark her a Defense char like Torbjorn and buff her accordingly then. I like playing Symmetra on some maps but once you place the turrets you feel immediately useless. You are too squishy for fighting and all you can mostly do is spam Orbs and hide in a corner waiting for someone to tag with your gun. Maybe there should be a way to set up "healing" turrets and "attack" turrets?
Winston - No immediate issues, but maybe his shield could use a slight uptick in health. I think this was nerfed in the beta because of the double/triple winston effect. Shield still feels useless when I see it used (I've never played Winston yet). Maybe its not being used correctly.