They also only absorb 200 damage each, which are all massively out dps'd by bastion. 3000 damage in a single clip is no joke.
Hell, the fact that they have 3 tanks in a comp is an automatic bastion pick for me. Have someone to protect his flank and you're golden honestly.
People keep thinking that bastion is a noob wall, but he also honestly serves a purpose as a tank buster. Reaper is better as that in most situations because he can do it on the offense too, has greater mobility and doesn't have as many hard counters, and also because people aren't going to run that tank heavy usually, but if I'm on defense and i see the other team heavily relies on their tanks I'll pull out bastion.
I'll give it a try next time I run into it and let you know how it goes. I know good snipers are a great Zarya counter, too, but the last thing I want to do when getting pressed on the point is tell people to go play a sniper. Weirdly, I've been getting a lot of games lately where no one wants to snipe, which is the opposite of how it was early on.