The tanks are so overwhelmingly strong that only your own tank can match the enemy tank. Keep your tank alive by all means, and if it is not alive, wait until it is. Try to kill enemy supports keeping the enemy tank alive, alternatively the enemy DPS.
There is no point trying to kill the enemy tank alone, and if it comes for you in any condition except almost dead, you should run for your life.
This is what they turned Overwatch into. It used to be so all Heroes were fairly well balanced and everyone had a fighting chance against everyone.