OK, let's clear up the confusion. The only Mystic Clean Rez is Spirit Dance. And as you state in your post, that is a 4 second cast, not 2. I throw out the 2 second all the time, but it is not clean as you seem to imply.
I said 2 sec clean rez for every healer except a mystic, whose is a 4 sec Spirit dance, 8 person blue aoe rez, of which you have to directly target one..yes i'm pretty sure i have rezzing down lol
Except the part that it is a Dirges job to rez before a healer, you have it perfect! Just kidding. I use the range and speed of my rezzes to my advantage and am often the first to rez ppl in raids. That means that my clean rez is often down and they do need Confront fear though afterwards, or Coldain Cureall.
I have ran a Mystic and a Dirge. In the heat of Battle the Mystic clean rez simply takes too long, from what Bentenn said the Mystic clean rez takes twice as long as any other healer, 4 sec is a LONG time in the heat of battle. All healers get a clean rez yet the Dirge does not and in most raids one of the jobs of a Dirge is to rez people so healers can heal, good idea to me. Yet the Dirge Confront Fear has a recycle time of 25 seconds or so which means if you rez more then 1 person everybody else is out of luck. Also Confront Fear gives a really good buff to the DPSers so it may very well be down because you buffed that big time DPSer.