The rub here is that Torbjörn's turrets, in the same general area as the Bastion, will aimbot Pharah if she's in range - thats if the Bastion doesn't see her first. And if there's a Widowmaker they might see her coming via infra-red, and if there is a Reinhardt those shots will be absorbed.
I can deal with a single Bastion fine, or a single Torbjörn turret fine, its when there are banks of the suckers, with simple support that things get very hairy. Its easy for a defense to set them up even as individuals, but its a slog to try and cut through them, even as a team. At least thats been my experience so far.
One time my team broke a nest of Bastion + TB Turret + Reinhardt barrier with a Tracer bomb. Not the most dependable or fastest thing but that's something I guess.