jkjk
For real though, when I give out comms to DPS, there's usually a reason.
Tanks/healers almost always get comms, so I try to find good reasons to give dps comms.
I run dungeons a ton, so I know how fast a run typically can go of most dungeons, and if it's not very fast it's either
A: the tank didn't pull very much or
B: DPS are big sucko and don't use aoe/aren't up to gear
If it's the former, there's almost no way in hell that I'm going to give the tank the comm, especially if it isn't their first time or aren't a new tank.

Giving comms to healer is different, it's easy to tell if they're doing a bad job. But it's also very difficult to tell if they're doing a good job too, unless you're looking for it.
If they're a godlike healer, they're probably going to get comms, but those are hard to find because you either get a clean run where nothing goes wrong, or a really bad healer.
Because of that, I typically don't give healer comms unless I've seen them do something.

DPS typically get my coms if I'm running dungeons with my friend who uses an... abacus to calculate damage and they're top DPS.
However, if either DPS fails to get top damage, I fall to either Tank/Healer because then you have a DPS that is big sucko.


Although, if there are no real good identifiers, BLM will 100% get my comm if there's one there