thing is, most annoying bastions are around a corner/chokepoint with cover
Roadhog's hook
D.va's defensive matrix (and self-destruct too if you really wanted)
Mei's ice wall
Genji's deflect
If anything, you could probably synergize these with a reinhardt shield for cover too
and actually, if you have a sneaky enough tracer or reaper, the back of bastion while in turret mode deals x2 damage to him
if theres cover, you could probably spam junkrat's grenades, or push them out with an ulti such as hanzo's, d.va's, or zarya's
hhhhey guys GENJI EXISTS U KNOW OR HANZO OR WIDOWMAKER
so you didnt even read this it seems