Work on your positioning. If the entire team is now pushing forward perhaps its best not to stay back as zen when 4 people are front and its time for you to go in given how high Zen's dmg out put is, not to mention how he can easily one shot any hero as well.
Sometimes, you will get outplayed; The enemy will have a smarter Genji/Pharah/Tracer that can work around you and because your team tried to protect you, they got killed in the process as well.
Here's an example.
The enemy Pharah is flanking you. Winston comes back, The Pharah's movement is great and now she's being pocketed by A mercy who's heal/dmg boosting her consistently.
That leads to Pharah getting a free ult charge not only from you but from Winston as well and getting a pick on a main tank/flanker tank as well as a support; turning the team fight to their favor.
Sometimes your own comp is not fit to deal with what they have, swap it up and continue the match. There's only so much even tanks can do against very good dps players.