Conjurer is a Class. SE wants Classes to be more for solo play. Therefore they should have some way of damaging the enemy(Aero, Stone).
"Why not give them just Banish and give all nukes to THM/BLM?"
1. CNJ lore still deals with the elements so it makes sense CNJ should have some control of the elements.
2. You can still equip Aero and Stone on THM just by leveling CNJ until you learn them.
3. Who actually equips all 6 elemental nukes on their action bar at the moment when your action points can go toward more useful abilities and spells?
4. It makes more sense for Fire, Blizzard, and Thunder to go to THM/BLM since those are the three staple spells for a BLM in the series.
5. Aero was a spell used by White Mages in FFIII.
6. Stone left for CNJ most likely for lore purposes and in case a CNJ soloing runs into something resistant to wind.
White Mage is a Job. SE wants Jobs to be for more party oriented activities. Therefore White Mages should have a good way of contributing to the party(Benediction, Erase/Esuna, Regen)
"But why does White Mages have that super nuke that uses all MP?(Holy?) I wanted to have that for THM/BLM WAHHHHH!!"
1. THM/BLM already has a lot of nukes as well as their own "super nukes" (Flare/Meteor and Freeze)
2. Notice the information about the WHM super nuke(Holy?) "Self AoE nuke and Bind". Pretty much a last resort if things get ugly since it's and AoE AROUND the caster that can Bind, giving the WHM time to back away from mobs attacking the caster if things get bad.
Enfeebles are still in the game except some of them are added effects with the elemental nukes:
Aero: Wind damage and DoT(Poison)
Aeroga: Wind damage and (Dispel)
Stonega: Earth damage and Heavy(Gravity)
Blizzard: Ice damage and Heavy(Gravity)
Blizzara/Blizzaga?: Ice damage and (Bind)
Thundara: Lightning damage and chance for (Stun)
Flare: Fire damage and DoT(Poison)
Also they could use the leftover spells for more DoM Classes since we only have 2 lol
Just my 2 cents.