If your team comp is suboptimal, and your teammates in the comp queue won't change, you have two choices:
1) Give up and throw the game.
2) Play your heart out anyway and hope for the best.
How am I being self-defeating?
If they won't switch, you switch. It's really as simple as that. I get that it gets frustrating sometimes, but actually reporting people to Blizzard because they lost the "race to lock in your favorite role" is just dumb.
Oh great, now I'm tilted again thinking about a match from last week.
Temple of Anubis. We've got a great team comp and get a good attack through - both points capped. On defense, our Reinhardt starts loudly getting onto us for not having a Bastion. "You have to have a Bastion to hold point A" he shouts. Thankfully, our team doesn't listen to him. We hold until overtime, but sadly we do lose point A and unfortunately get rolled over on B - because he's too busy yelling at us on voice that we lose A because we don't have a Bastion. So when the second set of rounds comes up, our Reaper switches to Bastion, and of course we get destroyed.
Seriously. I've never heard someone so adamant that you have to have a Bastion, to the point where he completely ruined what had been great team chemistry up until that point. It was so tilting.