In Overwatch If you have a full party it really pays for the highest level player on it to be a DPS.

It's possible to carry as a tank but only if you pick one who can do "plays" like a agressive Reinhart who farm ultis very fast or a Roadhog who hits hooks all the time and at this point you are basically playing a DPS with a large HP pool.

If your highest level is a healer you are in for a rough ride when the enemy Genji start going to town while your DPS misses all the shots.

Good DPS can sometimes win the game by themselves and sometimes is just what they do with a bit of luck.