With shield nerf just play a shield breaker from very long range (like hanzo)
Then kill bastion. Bastion is a none moving target. With shield nerfs he should be easy kill for all range dps.
If that not works because he gets into cover all the time(or lamp)
Since hitscan probably not that good in silver.
Play pharah. Flank around (like on junkertown, use houses to get behind/top of them and shoot it down when he gets distracted by the rest of your team)
Another way is use genji. Lots of silver bastions keep shooting at anything that moves. You can do lots of damage by using reflect, just make sure you dont feed.
You also can use sombra, but needs help of your team, just keep hacking the bastion, or shield.
Best way is to just all rush it , use map cover to get in brawl range and then all focus fire it Especially with zen debuff and bap lamp this works very well.
Just map position needs to be perfect and you need a team that actually wait till the ship reach the point you can all jump on them without getting noticed/tickling in.
Or build ults like dragon, or genji ult and kill it.
When tanks:
- play roadhog and hook him
- play rein and charge him to dead
- dva matrix helps longer then shields.(when you all decide to do the rush thing)
When support
- sleep dart helps to get close
- moira damage orb , build ult and use ult to kill them
- bap well placed lamp = better then shield, ult will also kill pirate ship when enough damage behind it
- lucio, maybe can boob away a shield. And can get your team in brawl range fast
- zen debuff makes him easier to kill and a full charged shot will kill a bastion. And easy to hit from long range.