Tracer and Genji can deal with it efficiently assuming you know how to play them good.
All the three snipers but especially Hanzo can deal with it as he can spam shields and make good use of his ultimate, the other two are more situational. Like on maps such as Junkertown with plenty of highgrounds and large space widow can completly wreck a pirateship by playing from behind it.
Deathball heroes like Reaper can do the trick very good as well. I mean, my favorite hero other than tracer/genji on some maps like hollywood is doomfist assuming I have dive heroes with me because it doesn’t really matter I can’t smack bastion around if the rest of the team also sit in that small space on point A with 6 people and you throw a crazy raging dude in there along with a moneky and a mech girl things will die and they will die fast. You can just instantly pick off the supports, come back and finish bastion unless your teammates do it for you.
And like I said, spam heroes like hanzo but also like trashrat and pharah can obliterate pirateships.
Now why pirateship is effective in lower ranks is because of the lack of coordination and that people just go in and die one by one. All you really have to do is group up as a team behind a choke and wait for them to come and when they do you engage hard so using mic and just emphasize the fact you need to group up might be a wise idea.
But like I said, if you want to deal with it yourself Tracer and Genji can do it. So with Tracer you just poke and build up fast pulse bombs which you stick to bastion. You often get 2-3 people and the only thing that can prevent you from getting him is if baptiste throws down immortality field, you can play around that by using it after pressuring it out or just stick it and IF he reacts fast enough they are still so low that you can one-clip the bastion or some of the other people making it easy for your teammates to just overrun the payload.
With genji you have two possible ways to kill it. Either by dropping down on the bastion while he’s shooting and using deflect and if that doesn’t work you can just wait for the nanoblade because it’s kind of lovely having 5-6 enemies stacked on that little payload because you don’t have to think much when you spam “ultimate ready” and ana confirms by saying “ultimate ready”, dash up, press Q, dash down, swing the blade and dash a few more times and everythings dead.
Heroes like McCree and Soldier can work just fine with let’s say a Hanzo or junkrat and hog/orisa/whatever spamming shields and just output more damage from range than bastion can deal to your team but that requires a team effort to break the shields fast enough so nothing you really can rely on doing.
Oh I forgot, Mei is a nasty hero and it’s not her ultimate that makes bastion cringe, even though you can use it to seal the deal so to speak but what you do is place the wall under Bastion and then the rest of the team can burn him. It works extra good on maps with highground because you can abuse HoG hook and just pull him after mei throws him up in the air but all in all, what mei wall essentially does is make him unprotected from shields, healers have a hard time throwing lamp or even heal as they will lose LoS and so on.
Sym can also be used in very creative ways. Maps like Hanamura if the defenders have bastion it’s very easy, all you do is teleport to point, above point or behind point and engage slowly or force them to come to you. The importance is just to not run around like headless chickens after teleporting. Set up, let sym burn the shield from an angle they cant shoot her (or you from). On payload maps you can just use her to teleport behind/above the payload they sitting on and brawl it out. And when you get ultimate up you win. Simple as that.
Oh yeah, you can always mirror it with a Bastion yourself and do more damage to shields which is autowin.
Basically, almost every hero can work. Some just works better than others in general and some requires less help from the team than others.
Just stay away from Sombra… Yes, you can use her and hack the world and win the game. You just need to be crazy good with her and if you are crazy good with her you wouldn’t be in gold/plat and you would be able to deal with a pirate ship much more efficiently with a Tracer anyways.
Because she wont get many hacks of if they play remotely close to decent due to shields and that heroes like Sigma and bastion simply can interrupt her hack so don’t play her thinking “all I have to do is go up and hack the bastion and hope my team engage and we win” because that’s not really what will happen. Like for Sombra to ever be useful you can’t sit in invis and wait for the perfect hack half the game you need to do damage constantly and consistently the entire game and build up very fast EMPs and again, not really that easy.
Like the only time Sombra is a nice pick is if you are superior to your opponents and just want to troll around which is why smurfs like her as they can spawn camp lesser skilled players.
The only hero worse than her is Bastion really and they can be forever alone together in the trashbag F-tier category with even heroes like Reaper and Sym laughing at them from their Tier above.