If this were in fact true, please explain why people DID NOT stack White Mages or Conjurers to do most endgame content but DID stack Black Mages for a fair bit of it. And all you are all proving is that you don't know how to use classes well. Did it ever occur to you that there are times when you don't even need regen to heal? That Stoneskin and and Second Wind and Sentinel (abilities a THM can use as well by the way) are more than enough to keep you happy and healthy, and in these situations (albeit not typical party play) CNJ is a better choice than WHM). In these cases, you can gain more damage output with CNJ over WHM. Period.
It is not my fault you all can't see the pros of using the base classes over jobs nor that you all can't have the foresight to see that while there isn't an enormous difference between base classes and jobs at the moment, the ability to use skills from all the classes on another class still does occasionally, especially for soloing and light parties, trump the job. As we gain levels post 50, the differences will of course, be much more severe...but that will take a level cap raise and other in game changes for you all to see. Again, sorry most of you are shortsighted or impatient.