Khan has an easier time taking care of other tanks. Use Fernando's charge to reposition yourself if he happens to be dissing on you, and try to protect your teammates from his ultimate by using your shield.
Fernando isn't the best at killing, but he can certainly pump damage. Working on the point, always fireball and flame groups, and charge into them to get behind them. Use the Scorch legendary to deliver as much damage as possible into groups.
If you happen to come across Khan, use the environment to your advantage. Get hits from a distance, run around, and get more hits on him. His relatively small shield lets you get more shots at him, too.