To everyone saying Widow's team has this godly teleport that gets her team to her under 4 seconds. Unless Widow is standing right next to her team, she almost never is, no one will be there to stop you. This is: How to WINston your way against a Widow
Landing on Widow does 50 damage, if you hit melee as this happens you get another 30 damage. Widow is now at 120hp, you star using your primary. This does 20 rounds a second, each round doing 3 damage, and now you have a dead Widow in 2 seconds. If you are dying to Widow, I want to know how you are accomplishing missing Winston's auto aim primary. Its a feat that is mighty impressive.
Lets factor in Winston's health and shield now. Winston has 400 health, 100 armor, and a 600 hp shield. this gives him effectively 1100hp. Widowmaker at full charge does 150 damage, 300 on headshots. She has to headshot you twice for you to go down, six shots and a pepper with her primary or poison for you to go down if you use your shield to block. So unless you are running straight at her in the open and then stopping and sitting there watching her as she shoots your shield then please explain to me why are you playing Soldier 76 when you chose Winston?
"But darklin, how do I get to her? D': " Well let me tell you about this amazing thing called the Jump Pack and almost as equally important, alternate paths!!!!!! Winston has this ability where he can jump in an arc at a fairly quick speed. Combo this with his shield and you will pretty much barrel through any choke point. When you do this their team will either ignore you or go after you, both being good. If they ignore you, you can get some hp if needed, wait for your shield to be available, and then walk to a spot where you can just jump up to a Widow unnoticed. If the opposing team feels like they need to chase you then you effectively gave your team a huge open window to come in and hit them hard for that mistake. Like I said, both situations are good. Now, if the Widow is that amazing to where she alone can hold off their team supplement a Rein to help push forward. The Widow will die or run, either way you nullified the Widow. Hooray!
So what about alternate paths you say? Well let me tell you. See every map has a path that does not go down straight into your enemies bullets. Some maps do have these really dumb choke points but they always have at least one alternate path to go through. Unless their team is dedicating a bunch of people to those spots Winston can get through. Even with Widowmaker's Infra-Sight, if they see you take the path and follow well I already explained it before.
So from playing with Pugs to playing with a team, Widow is a chump. If you are in group and your team is not capitalizing on Winston diving the back, get a better group. Or learn to coordinate.
I need to head somewhere so I can't finish up. Apologies for errors I did not catch on my quick skim trough. Maybe part 2 later with more detailed situations.
TL;DR
Use Jump Pack and alternate paths to get to Widow. You are not Soldier 76 god dammit.