While I also agree with the OP, I think it's important not to change CNJ and THM so drastically that players that are used to only playing one or the other don't experience a sudden role-reversal that upsets everything that they're used to in terms of gameplay... kinda like what happened with GLA and MRD in terms of who was the better tank - I was used to GLA, but now I have to level MRD because I can't parry with a shield equipped anymore, or hold hate unless I'm spamming Storm's Path? Really??
I don't play CNJ or THM very often (I only leveled them to get the good Cure and buff spells for my GLA to tank better, lol), but as of right now, CNJ to me seems like it's trying to do everything mage-wise (access to all the elemental spells, healing spells, multiple DoT's, some buffs and debuffs), while THM seems a bit gimped in comparison (Banish/Scourge serve to improve Astral/Umbral damage, which has yet to be fully explained in regards to the elements; Sacrifice is the only healing spell that can target allies and is no longer AoE, Drain only works for yourself; the Absorb spells also only work for yourself until you use Initiation, etc.).
With that in mind, here's a list of possible changes to these jobs I could happening:
1 - Give both CNJ/White Mage and THM/Black Mage access to all 6 elements. CNJ/White Mage does Astral damage with all of their spells, while THM/Black Mage does Umbral damage with theirs. I could see Holy and Meteor tying in well with this, if implemented.
2 - Give both CNJ/White Mage and THM/Black Mage access to all 6 elements. THM/Black Mage gets spells that do burst damage (Fire, Ice, Thunder, Water, Stone, Aero), while CNJ/White Mage gets DoT spells (Burn, Frost, Shock, Drown, Rasp, Choke). Although both jobs need to avoid pulling aggro, I think this setup would allow White Mages to still be able to do damage in between heals without incurring too much enmity or outperforming Black Mages in terms of burst damage.
3 - Completely new spells for each job. CNJ/White Mage gets things like Benediction, Auto-Raise, Holy, Reflect, Barrier, Shield, etc. THM/Black Mage gets Comet, Meteor, Armageddon, Ultima, improved ancient magic spells, etc.
4 - Keep the current proposed changes, then later add new Disciples of Magic (Red Mage, Blue Mage, Time Mage, Sage, Summoner, Arcanist, Scholar, etc.) to make use of spells/abilities that may have been removed. In the meantime, revise the current elemental "wheel" if necessary, and don't leave players in the dark about how spells, elements, polarities, moon phases, the in-game calendar, and everything else works in relation to each other.
Any thoughts? My ideas probably aren't the best in the world, but SE kinda shot themselves in the foot in terms of how they're going to "fix" this, lol...