IMHO key requisites for vSS:
1- one tough main tank
2 - one smart off-tank
3 - one strong healer (i mean strong in heal output)
4 - 3 smart DDs that can perform the ice tomb mechanich
A medium DPS of 40K might actually be better not to overlap mechanichs (if the dragon starts to fly when you still have atronach around u wont be having a good time).
This fight will be especially tough on healer and you will need to perform mechanich and kill adds in the correct order if you want to win it.
If you ask me it's the best one to start from/farm for gear if you can't close the trial.
1- one REALLY tough AND SMART main tank
2- one REALLY smart off-tank
3- two REALLY strong healers
there are easier mechanichs in here for DDs but it's very very harder for tanks and healers since this boss hits like a mack truck.
The off tank will have an helluva job in placing flame atronach in the correct positions before you kill them (else you'll wipe) especially with medium DPS (while with an high one it gets better since the lava pool gets cleansed when the dragon breath while flying.
1- 3 strong DDs for portals
If you can kill the other bosses you can kill this with the very same group. only requisite here is that the 3 DDs assigned to the portals are capable to handle em AND not die (else is wipe).
Since the tanks will swap a lot it's gonna be an easier job on their resource pools (one can recover mag/stam while marked for death) and even the breath attack is not as strong as the fire boss one.
75k on the iron atro (it's all we have to go off of on console since no CMX) is a good starting point for this trial. Damage is so insanely easy to come by, there is no reason someone shouldn't be able to hit that, even without bis gear. If they don't have the discipline to achieve that level of damage, then they likely don't have the discipline to follow mechanics in this trial and complete it without a sizable carry. That may sound harsh (and it admittedly is), but after suffering through this place over and over again on a healer while "helping" lower level groups try to clear it, I can honestly say it stops being fun after the 8th, 9th, and 10th wipe on each boss.