A meter showing you your own damage would be great and I think really should be added to the game. There's currently no clear indicator of just how much damage you're actually doing (except when soloing) and there needs to be. That's something that can help you improve. One showing you everyone else's damage, on the other hand, does not help you improve.

This isn't like a single-player game where you're controlling the actions of a whole team. You're only controlling your own character's actions, and that's the only damage you can improve on. It's up to your teammates to maximize their damage, not you.