FF1: Quake attempts to instantly kill an enemy by swallowing them into the ground.
It is not an earth elemental spell.
FF3: Quake is a Level 7 Black Magic spell that causes major Earth-elemental damage. Only the Jobs Black Mage, Magus, Sage, and Onion Knight can use this spell. It can be bought in Doga's Village and in the Invincible.
It is not exclusive to BLM, though it is black magic in FF3.
FF4: In this version it is a non-elemental spell that damages all non-flying enemies and ignores Reflect.
Non-elemental
FF6,FF7, FF8--Quake is an earth elemental spell, but is not really attributed to a "class."
FF11: The only game where Black Mage exclusively receives Quake as an earth elemental spell.
FF13: Is not a spell, but a technique (that does deal earth elemental damage) learned by pretty much every character, in different roles of the crystarium.
FF Tactics: Quake is Planar Magic.
Crystal Chronicles RoF: Quake = piling Fire, Thunder, Cure, and Clear. It inflicts stun on the enemy
Crystal Chronicles EoT: A pillar of rock erupts from beneath the enemy, sending it flying into the air and inflicting a stun effect after landing.
See the trend?
Googling and reading FF wiki might not be the best way to argue.
If one class had all elements, then either that class would be grossly overpowered (having an advantage against almost any mob) or the bonus from using the "correct" element would have to be so minimal that it barely existed (as you would ALWAYS be using the mob's weakness).
This is an issue in and of itself. There will almost definitely be a DD job that comes out of conjurer at some point. The game isn't even launched yet. The job system is barely developed.
I don't follow. CNJ is a decent attacker and decent healer. WHM is a great healer and decent attacker. In both cases, DDing takes away from ability to cure, and vice-versa--you can't deal decent damage WHILE keeping a party alive in difficult content. THM is a great attacker. Both are unique, and neither is making the other useless.
Divine spells are iconic to WHM, but one could argue the same for earth, air, and water spells
The THM lore that we know from 1.0 is butchered; I wasn't in alpha, but I believe that will change for 2.0. I'll try to find the dev post I'm thinking of.
CNJ lore, however, never was truly butchered. Though I argued that it was at one point, the fact is we retained control of the three elements that really appeared in the Shroud (and if you're at all familiar with the lore, you'll understand why those would be the three that matter).
Out of context, the bulk of this segment could describe ANY job. I think you vastly overestimate how "fun" it would be to have to stalk out the wiki page of EVERY mob you encounter to determine its weakness so you could optimize your damage.
No one else took you up on this offer, but... how much do you charge for a half hour? ;D