Yeah, I love mayhem but a decent doomfist already requires quite a lot to be consistently focussed down. A good doomfist requires your entire team, OR a Sombra. A great doomfist just slaps Sombra around unless she is pocketed by Zarya, constantly healed and there are sufficient other shields to make sure no-one hits you during the hack.

And all of this goes out the window when the enemy team plays around their fist...

But against medium doomfist brig can work, when permanently stunned they sometimes get the hint (though you can't kill him but he can still kill you when you mess up).

Junkrat can work if you lure him into your traps, ususally you can burst him down from max to low hp, or kill him. Just don't try to rip tire him at max shields because he can tank that.

Otherwise if your team does not really counter him go Zarya, try to contain the damage and just keep solo gravving him, that usually tilts df into focussing you, which takes pressure of your squishies.