There are a few places where there is only one way through but that is the worst IMO. However the beauty of Overwatch? switch characters to counter it. Get a mercy to heal the team as they take damage from the turrets, a widowmaker to snipe them, a reinhardt to provide cover, Pharoh or Hanzo to go over the top, a roadhog or tracer through the door and get behind them. The biggest mistake I see randoms make it shooting the turretts when you should shooting the Trobjorn. Once he isn't around to repair the turret they are easy to take down and objective A is too far away from the spawn for him to get back in time. Then again, randoms so rarely focus on healers which annoys me. Take the healers down first then you take down the offensive/defensive characters.
Playing a ranked match the other night, we had an overtime match to attack and the defend team had 2 turrets and a Bastion with a Reinhardt shielding them all. A couple of changes from out intial choices of character and we rolled straight through to victory.