Well Gunner was already nerfed and it might need a little more tweaking... anything beyond that is just ruining the class and im super sure alot will not be happy with that and just quit entirely so nerfing gunner more needs to be done veryyyyy carefull.
Gunner has lots of iframes, an automatic "unbreakable", extremely self-sufficient, lots of HP, and self-healing. It should not be one of the highest DPS classes, it should be pretty far down. It's not reasonable at all to keep it stronger by 50% of all other classes, or even 20% stronger for that sake. There's no argument for having gunner being the highest DPS class.