Mathematically, Winston wins. Tracer can do 240 damage per second with a one second reload. If all of those are head shots, then she can do 480 damage. Winston also has 100 armor, which blocks 5 dmg per pellet. Her gun fires 40 pellets in one second, with a max damage of 6, which means against armor she does 1 dmg per pellet, or 2 per head shot. Given that, Her first clip does 80 dmg. Her second clip does 20 damage to the armor, and 360 damage to him (assuming head shots). So in 3 seconds, you've done 480 damage, now just a melee. So it takes 3 seconds to kill Winston, at max damage, landing all of your shots, and all of your shots are head shots. Winston does 60 damage. So he kills you in 2.5 seconds. Now if you recall... and blink... and he bubbles and jumps...

Basically, you could be a Winston, but he definitely has an advantage. The reason you probably see him as so squishy is because you do a lot of damage all at once, which is a huge problem for Winston because Winston should always be watching his health while diving, and he should jump out when he gets low. If he doesn't see you and miscalculates, then you do a bunch of surprise DPS quicker than he can react.