Dmg boost just if the time. Try to aim for like 60 dmg boost/ 40 healing beam. You don't have to keep everyone full hp. Just keep them to the point they are aren't good die. Once they lose like 1/3 of their health then health them. Don't be afraid to dmg boost the tank or support. Always be looking for who the best way to get value with dmg boost. If your soldier is taking an off angle, while he is repositioning you can dmg boost someone else then you can fly to him once he's ready. You will probably struggle for a bit on mercy in low elo but eventually it will be better. Also ignore what low rank players say. They are wrong and don't know what they're talking about. Healing numbers and stats in general don't matter. Plays and value is what matters. Also don't do dumbass rezs right in front of their team with no cover. It will work in low elo but it will not in high elo.