With the caveat that I have not yet gotten to the Heavensward jobs, I have to say thaumaturge has been my least favorite class.

The class spell rotation is so repetitive and you are punished if you ever need to move, which is all the time when you are questing. I've leveled a glad/paladin/ marauder, conjurer/white mage/scholar, and a pugilist/monk who is also a lancer/dragoon. None of those were as miserable to level as a thaumaturge to 26.

The class needs its survivability bumped by either allowing thaumaturges their own kind of magic shield, or giving them a low level spell which drains health from the enemy which can be used while moving, or giving them an instant spell which allows them to get distance from the enemy(ies) after casting a Blizzard II.