If they want to punish DPS Moira players, I’m don’t think a fluctuating damage attack would be the idea.
I’d try something more like this: Moira now has ammo, but it only depletes when she’s at full heal spray meter. In addition, she also gains heal spray resources when damaging shields with biotic grasp (even if it’s at a reduced rate). Forcing Moira to go into a reload animation would curb some DPS Moiras, or at least hinder their “hold damage and forward buttons for results” gameplay.
Then again, I’m not even sure it’s a problem that needs to be solved, so even my idea is kinda… meh.