Looking at the Conjurer before these changes, it was the mage that harnessed the power of the elements. While yes it had all the resources necessary to be a good healer, it also had the resources necessary to be offensive. In my opinion, post 1.18 the Conjurer class was offensive with an obvious slant toward support.
Looking at the Thaumaturge before these changes, it was a mage concerned with the balance of life and death known for its Light and Dark powers (Banish and Scourge). Along with its array of draining and enfeebling attacks post 1.18 Thaumaturge was offensive with a slant toward enfeebling.
Thaumaturge advancing to an offensive caster looks to be a fine choice as far as I'm concerned. However, Conjurer had the capacity for both having not only support skills but a full roster of elemental abilities. I consider it a fundamental change to:
1.) Take Conjurer with the capacity to be both offensive and supportive and watering down one facet of its abilities by taking several attacks from its arsenal.
2.) Take Thaumaturge with the capacity to be offensive or an enfeebler and totally eliminate enfeebling and draining skills from it, watering down one facet of its abilities.
3.) Totally remove Scourge and Banish from Thaumaturge and replace them Fire, Ice, and Thunder, while not hampering its offensive capabilities, totally alters the lore of the mage that revolved around the balance of life forces.
4.) Totally remove Sacrifice, the only native heal to Thaumaturge forcing it to cherry pick a skill from another class if it wants to support and possibly to solo. (I say possibly since I don't know how the HP skill it's been given will function).
I've said this many many times, but the Jobs were created as the specialist roles. The problem that I see is the classes, especially in the case of mages, have been overly specialized in the process making the jobs seem redundant.
Although its obviously too late and would never have happened, it would have made more sense for Conjurer to split into White Mage and Black Mage with Thaumaturge advancing into a different mage class.
Another possibility would simply to have, for example, let a Conjurer advance to White Mage and simply lock out elemental attacks when playing the White Mage role and likewise lock Thaumaturge into a specialized set of skills as Blackmage to suit that role. In this scenario Conjurer and Thaumaturge as CLASSES not a jobs would still have the liberty to be offensive or supportive but obviously not overshadow the White Mage or Black Mage which have specialized skills and most likely traits for those roles.