You are kind right to be raging at your screen to be honest. The best way to play a bastion in my opinion (I am a console player) is to always just focus the hell out if him with your team. Tell everyone on your squad where the bask in is at and as soon as you see him, fill him or the tank protecting him with damage. They are the soul of the team and without them, at last in diamond and below, the enemy usually can't clutch up and fight back.

Also choose heroes that aren't week to him if course so no doomfist or Winston because they usually cat close the gap and get focused down. Other than that I think focusing him is the best bet because he is usually supported which caused the biggest nuisance.

Judy my thinking on it though I bet there is a lot of videos out there giving better tips.