I think I'm finally starting to really get how to play as Winston.
If I'm in the center of the fight, I'll be the first to go. But if I pounce away when I see the enemy coming in, and then pounce back when the battle starts, I can get double and triple kills all the time.
I feel a little scumbaggy doing it, though. It's like, "Here, team, take this bubble while I run away from the fight only to come back when I can help clean up."
The problem is, if I don't play him like cavalry, he dies way, way too quickly to be anything more than a speed bump.