Please replace commend with

[Roda]

They have actually said in interviews/liveletters that they were considering putting a system where the player can monitor their own DPS, but they are hesitant about it.

I think the commendation system is fine. Players just aren't incentivized to use it mindfully.

The problem with having a private personal dps meter is you have nothing as a point of reference. Someone might think their X dps is just fine, but just not know that everyone else around them is doing X + X(0.7) or whatever. Same problem as back in the day when people were looking at the threat meter for gauging their own dps,and them being at the top only because the more skilled players were using their threat dumps.
A private ranking system (where you don't see anyone else's rank) helps you gauge how your performance compares to the average over time.

(And yeah I prefer ranking to letter grades. Because its more flexible and less work to have to tailor it for each job, role, and encounter. Crowdsource the performance feedback.)