The one thing I like about going into the DF as a tank is, there is a good chance I will get a healer like me (that enjoys the run more than they need the points), and so, which only leaves the DDs as possible DBs. And if one shows themselves, they usually leave the party by the first boss, and are replaced (90% of the time) with a more amicable player.
My favorite was, I did a DF run on WP, and at the birds before the first pugil, I waited for the tonberry to pass. Not a bad idea for a DF run, and gives you all the time you need, with no further possible delays. It is actually the way I learned the run, and I have found it to be a good way to gauge a party (Since then, I have learned that if you can kill one of the first two birds before the tonberry moves, you are fast enough to out-run the tonberry).
One of the DDs said the pt was moving too slow, so they left (incuring a 15 minute wait). A new person popped in within 1 minute, and we finished the dungeon in <15 minutes (So, before the person could queue up again). We had a good laugh at the DBs choice.
When they add in player ratings I have a feeling things will get a little more polarizing. You will get people who are even more impatient (Sucks when you DF with a full pt of a FC that needs a pickup healer or tank, not sure how DDs feel), but you may also find parties where people actually enjoy a group that plays for the enjoyment of playing.
I already know that I will never vote for anyone who complains about party speed, nor will I vote for any DD that dies to trash mobs. I will however always vote positive for pretty much every other pt member, and from there, will figure out a rating scale of some sort, and hopefully will be able to live up to other peoples standards.
But yeah, I would say over 50% of my DF parties has at least 1 DB. So there are still more amicable players than DBs, but, I wouldn't call them rare... They are pretty common.
I even know a few personally that I try to avoid pting with. It is really rough when you are learning something, and they tell you to either go as a DD so they can carry you, or they spend 5 minutes telling you how you should avoid a move as a tank because you get hit by a slipstream at the same spot every time (The tornado phase of Garuda, which I have since learned from another player (who spent 30 seconds at the start of a fight explaining it) that if you tank her at the flags, it is 100% avoidable, but if you tank her by the rocks, it is a pain to avoid).