Good thing you are 6 on your team then, so the shield really dies instantly with a Bastion on your team. Unless of course, your team knows shit and refuses to shoot the shield..
Had a game yesterday, I was bastion, a Winston and Reinhardt came with the caravan, I just sprayed them down before they could even turn around and run, with ofc my team helping.
Not saying Bastion is hard to kill though, just pick Reaper, Tracers, Hanzo, Pharah, Widowmaker and make his life a living hell. Or Genji, McCree. Well, pretty much anything :P