I'll be honest. If I com a DPS its because the both the tank and healer failed to impress me, or more likely, one of them failed and I took the other spot myself.

There are a lot of things a DPS can do right, not dying, keeping their rotations optimal, using any utility like res or peloton. But unless the tank and healer are both bad, the DPS isn't getting the com.

Why? Because in a group where every one performs well, the blue and green jobs had the additional distinction of helping to make the duty pop sooner. I know a lot of people might think this is unfair. But as I see it, FF is not a single class game, there is nothing stopping people from filling the adventurer in need role.

Besides, although I priorities coming healers and tanks, I really don't think this is as common as most people seem to think. My experience as a healer is that the more I excel and compensate for a bad tank, the less likely I am to get any coms. My experience as a tank is that the more I excel and make things easy for the rest of the group (by mitigating damage and positioning mobs for aoes and positionals) The less likely I am to get any coms. And even when I assess my performance as a DPS as having been horrible, I still somehow get coms.

Honestly I think I average about the same number of coms irrespective of the role I fill. I think the reason for that is that no matter what role you play, if your doing it well, your making it easier for the other roles to stand out as well.

If as a healer you successfully keep the tank with a woeful minimal ilvl alive through all the big pulls, then the tank stands out for doing so well despite their handicap.

If as a tank your properly geared, roll your cooldowns and position the enemies to allow dps to best use their positionals and aoes, then the healer and DPS stand out for killing everything so much quicker.

If as a DPS you avoid standing in bad, are properly geared and maintain the optimal rotation for your level range then your tank stands out for taking so little damage (everything died before cooldowns wore off)

So at the end of the day. If you want coms for some reason. Say hello, be friendly, have a nice glam, make a joke or two and keep your fingers crossed. But dont worry too much about what role you play, because when you stand out enough to get a com it often has as much to do with how well other players did as it dose todo with you.