I think Bastion’s problem is silver players.
They’re smart enough to play against Bastion, but not smart enough to play with it.
Like, they understand how each character should react to Bastion, but they never think how their actions are going to affect their most powerful yet vulnerable DPS source.
PSA for silver players: On defence, never retreat behind a sentry Bastion just because two or three enemies are coming towards you, unless you are on a sliver of health. The Bastion will die without getting any kills, and the enemy will be at a 1-player advantage as well as having gained ground. Keeping the fight away from Bastion but still in view will result in everyone being mowed down in seconds.
I’m at 1900SR, so I play with both silver and gold, and I find that silver players will happily leave Bastion open even to small pushes while gold players hold their ground for the 5 seconds it takes for everyone to run or die from the hail of bullets.
Bastion seems more viable in gold than in silver, but since most people play silver first they learn not to play Bastion.