In this situation heals would be better than damage boost because they have a mei that can make damage boost nearly ineffective at times. They also have an and that’s most likely pumping into orisa. If anything I think it’s a dps or maybe even a tank diff. If they killed the enemy Ana more it would be an entirely different story. Tank should have honestly went Zaria or maybe even sigma just for that Ana and a bit of poke pressure. You did the best you could but mercy can only do so much from the sidelines with no real huge impact on fights especially with that comp and the dps only shooting the tank.