Until RDM gets a useful buff, there's no reason to use it over WHM simply because WHM can do the same job and neither job has MP issues these days if geared properly. RDM brings Dia III to the table (-5% DEF over Dia II), but it has to sub Scholar or White Mage for status removal. My poorly geared White Mage mule subs Thief in Dynamis and keeps me alive through 5-mob Aeolian Edge spamming pulls without downtime.

Temper could have been that buff, if it was 3~4 times as potent and party-target. It isn't, so it's not.


I've turned the problem with supporting role RDM into this handy decision tree:
1) How much Refresh do you need for what you're doing? (2 - A lot!, 4 - Not Much)
2) How hard does what you're fighting hit? (3 - Really Hard!, X - Why do you need a lot of Refresh then?)
3) End: Okay, go WHM/RDM
4) Is what you're doing affected by Treasure Hunter? (5 - Yes, 8 - Not rly)
5) Are there any status debuffs? (6 - Yes, 7 - No)
6) End. Go WHM/THF
7) End. Go RDM, WHM, or SCH/THF
8) End. Go any job with Cure IV

So if you were going to gear one job with Cure IV for the purpose of filling a supporting role, White Mage should be that job.