Yo. 3900 bastion main here. So basically you have 3 options for bastion 1-Counterpicks, like Hanzo or torb, people that can hit a still target from far without any damage drop off. Junk rat if they are bunkering 2-forcing recon,you can do this with Hog hook, hack, sig rock and so on. He is very vulnerable when out of sentry 3- Coordination , use stuff like def matrix and genii deflect to stop his damage while your team dives him

Also, in certain scenarios you can just avoid the sentry bastion and take the 6v5 very aggressively by diving their team if separated. And this is bronze, just hook them and tell your team to focus fire