A bit off topic, but if you pay attention to the job quests associated with both CON and THM, Thaumaturge is definitely the darker of the two classes. They're occultists. Conjurers are more nature-loving treehuggers. These aspects of the classes have been in place since day one and as a result it seems clear to me that the intention was always to have THM as the BLM style mage and CON as the WHM style mage.
The unfortunate part is that the classes seem to have been mislabeled in localization, leading to confusion. Also both classes were given a mixed repertoire to prevent nukers from being excluded due to lack of healing capability, leading to further confusion.
Make no mistake, if a line is drawn in the sand between Healer and Nuker, Conjurer will be the former.