I did mention support from his team right? A bastion in that position should have a Widowmaker backing him up, in a case like that Pharah won't even get close to him.
Junkrat can definitively work but he's not exactly the character that has the easiest time sneaking behind enemy lines.
Hanzo is probably the best pick there but if you pick him reactively to counter Bastion, you have a lot of catching up to do by having your ult reset.
Bottom line the biggest problem with Bastion is that on maps like that, it takes a coordinated team effort to counter a single character from a position where his own gameplay requires absolutly no skill whatsoever.
This is why i'm saying he's not overpowered though, cramping up like that in a corner like that works great for pub stomping, but a real team will easily have the coordination to get rid of him. Forget about pro play, he's going to be worthless at mid-elo on the ladder. Because there's absolutly no skillful way to play the character at all.
The only real "PoTG" i've ever seen from a Bastion is this :
https://www.youtube.com/watch?v=FIlzzjEjj6M
But its the character in its absolute prime, there's nothing else you can really do more with him, except maybe get a pentakill during that ult? The rest of his kit is completly binary. I still have no idea how Blizzard thought BEING a turret would be good gameplay.
This is why i hate the character so much.