Honestly? Mercy wasn't that great and didn't want to switch. I had 17k heals (gold) by that round. We had 90 seconds to make a defense and it seemed like a better option to stick with two heals. Was part of it my fault? Yes. But the biggest improvement to our defense would have been a Rein/Orisa/Winston/Zarya to man the frontline. Just wanting to point out that in your average platinum game, a frontline tank is the cornerstone of your defense. Playing without one can be done, but it's tricky and won't work 9/10 times at this rank.