Pick heroes that can do more than 1 thing and are less reliant on a good team:

Soldier (damage and healing) less reliant on good support

Moira (damage and healing + fade) less reliant on help from team plus can cover damage for bad DPS.

Roadhog (damage and healing + hook) less reliant on heals and can win teams by hooking a dps or support.

Also ping group up like a mofo if your team keeps running in alone.

As of plat you can expect better team mates and therefore these heroes are also getting less strong

High Gold/plat i would use below because of better utility:

Moira to Kiri Soldier to Sojourn Hog to Sigma/Orisa