There is no back line and support in bronze.
Sorry had to do little joke, Winston is good as any other hero,but I found two heroes incredibly powerfull in bronze and silver, able to carry whole team because of their kit. Its zarya and Mei. They are best to carry there in my experience.
In that case you kill them all because Winston is always MAXIMUM CHARGE. Mei will probably be better because bronze players seem terrified of bubbles so charge will be tough to maintain.
Looked at your stats, try practicing your tracking with Sombra a bit, or get closer to your targets.
No vod so I cant say what exactly is keeping you in bronze, however practicing aim/staying alive is the first step toward climbing c:
It’s tuff being green.