I think a lot of support mains underestimate their value. You're not just a heal bot and the exact support you pick is really important too.

All too often I see supports flat out refuse to play X support, literally because they don't want to. And ok, sure, you can play what you like. But the exact same people will be very quick to ask the DPS to switch based on the situation. Sometimes the situation calls for a Mercy, if it would increase your chances of winning (for example, if you're playing Bastion Bunker or Pharah) but you flat out refuse, you're kinda soft throwing. Likewise, if your team needs a defensive ult and both your supports are intent on staying Baptiste and Moira, that can also be soft throwing if taking a Lucio or Zen would prevent a couple of lost fights.

And likewise, if you're expecting to keep your team alive and that's enough, you're not really doing your job. A sleep on a nano blade, even if you only successfully do it once, will flat out carry a team fight. 1 regular cool down for 2 ults? That's insane value. Same thing can be true of Immortality Field or Rez.

Don't go into games presuming your team is incompetent. Presume they're going to carry and play the support that will help them carry best. That might be Mercy sometimes, other times it will be Ana or Baptiste.