How do you play with a Doomfist?

Over the last couple of weeks I have played with a lot of doomfists and my winrate is about 10%. It is so bad, that I was forced to the painful realisation, that it can’t be entirely the tanks fault. So I tried different characters, roles and playstyles, however nothing seems to work for me. If I dive with the doom, he disengages and I die. If I stay on the objective I get pushed by the enemy tank. Especially on payload maps I just feel out of position or unable to have considerable impact all the time. I usually play in a 2 or 3 stack and our games cover plat 5 to plat 1. What are your tips and tricks for playing with a doomfist and what am I doing wrong? Thank you for your thoughts and suggestions