My problem with commendations is that they're functionally the equivalent of a car's horn; as a humor writer once put it, car horns are used to communicate a variety of different messages including "the light is green", "the light was red", "I hate you", and "this vehicle is equipped with a horn". And there's not always a lot of way to distinguish between which one was meant.
Did you get the comm because you played your job well? Did you get the comm because you were funny in party chat and made some good quips? (I am convinced this is why I used to get comms in the old Praetorium, like when I narrated all the cutscenes in chat as if they were a Sir David Attenborough nature documentary one time, or when my co-tank on one run and I spontaneously pretended to have Gaius and Nero on a talk show called 'Tank Talk: Where you get to talk with tanks!') Was it because someone liked your glam? Were you the only person left when someone came out of a cutscene? Were the other people a pre-made and they all just commed you? Who knows!
I ran into someone in a roulette once who was named "Kwehstopher Warken" and dressed as a giant chocobo, and I commed him because that made me laugh aloud when I finished loading into the instance and saw that.
And sure, there are times when it's not a mystery. You're a red mage and you manage to rez the healers when they're both down? If you get commed, you're probably not confused as to why that was. Stuff like that. But I'd say that easily 80% of the time you may not know why a comm was given. So actually using comms to actually measure anything -- including suitability for mentorship -- seems like trying to use the wrong tool for the job.
After all, the comm might just be the equivalent of a car horn, communicating "this game is equipped with a commendation tool (and I'm going to use it on someone)!"