Maybe they should just remove damage boost from the game except as ultimate abilities. Give mercy damage resistance tied to her heal beam, and make her alt click fire her pistol.
Full mercy suggestion here (That has nothing to do with resurrect or her ultimate, except indirectly.)
Except in this context maybe the damage boost AoE would be replaced with something else, like damage resistance and where they overlap would be damage boost instead, making it harder and more resource demanding to give someone a damage up, and only in a specific spot, or it’d be something else entirely. Like generating a barrier along the intersection, or granting shield.
Mercy is in need of a rework. She’s unfun, and both she and other heroes are held back around her balance.