You're way overthinking it. Commendations don't mean jack. Most of the time as a DPS you will get one comm in four-man content and that is because the other DPS simply give you their commendation blindly. Meanwhile the tank and healer blindly commend each other unless a problem arose during the duty. There's no criteria for 99% of people, that's just reality.
In 8-man content it might be slightly different (maybe someone is running ACT and gives it to the top DPS or whatever) but generally comms mean nothing.