How to counter 3 healer?

I'm new to hero shooters; I played about five hours of OW2 when it came out. That being said, I'm decently good at games; I've solo-queued all the way to Platinum I. Recently, I've been in games where my team was running either a 2-2-2 or 1-3-2, and we were stomping the other team. All of a sudden, there's a shift where we can't get kills anymore or aren't pushing the objective, and it's because the opposing team switches to three healers. It makes sense that that would make it harder to get kills, but how does that also lead to us dying more as well? Many times, I've told teammates to switch to a third healer to at least match the healing, but it's always a DPS who isn't doing enough damage to begin with that says that won't help. Doesn't it make sense to people that staying the same won't work? It's very hard to outdamage three healers. But I don't know; just my thoughts; maybe I am wrong in terms of matching their three healers.