How to tell if you're doing well (DPS edition):
[ ] Are things that are supposed to die dying?
[ ] Are you using your cooldowns when you can and/or when it's appropriate?
[ ] Did you avoid all avoidable damage unless the healer/raid leader told you not to?
[ ] Did your group successfully complete the encounter?

If you're 4/4 on these, then congratulations! You're playing the game adequately, and no one has any right to tell you otherwise.

If you're not, then you need to work on your own gameplay.

There's so much more to being a good player than putting out good numbers. Putting out good numbers is a good thing, but I would much rather take someone who knows how to avoid AoE, or who plays their class to boost the rest of the group, than someone who's so fixated on their rotation that they die 50% of the time.