Challenge accepted.

Jobs are the end-all-be-all of end-game cooperative content. A paladin, for example, has higher base stats than a gladiator. More than that, those higher base stats are also specialized to a specific purpose: they have higher strength, dexterity and vitality which provides more damage output, a higher chance of blocking attacks with their shield and more damage mitigated during a block, and a higher maximum HP pool. They also get five job-exclusive abilities which are specifically tailored to paladin's purpose: to be the best single-target, damage-mitigating tank in the game. The cross-class skills available to them (gladiator and conjurer) are those most important to a tank (additional hate-generating abilities as well as low-level cures and buffs to augment their defensive capabilities).

In all my time running endgame in 1.x, the only class that ever got use was thaumaturge, and it was only in very rare circumstances. It was basically so that thaumaturge could use sacred prism (a conjurer ability that made the next spell area of effect) with sanguine rite (a thaumaturge ability that gave 50% damage reduction and converted some damage to MP recovered) as a 5-second defense againsty very powerful attacks (like Nael deus Darnus's Megaflare or Ifrit (Extreme)'s Hellfire. For reference, neither of these spells exist in A Realm Reborn. Occasionally you might also bring a thaumaturge just so that they could sub raise.

Jobs are specializations for specific roles. They're very good at doing one thing, and not very good at doing anything else. They get access to cross-class skills from only two classes that are meant to supplement and emphasize their strengths. This makes them ideal in cooperative, party situations. Classes are good at one or two things, and they get the full range of cross-class skills to augment their weaknesses. They excel at nothing, but they lack glaring weaknesses.

All end-game content that we know of is designed to be cooperative, and therefore jobs will be preferred. You will spend more time with your job's soul stone equipped than you will as a base class.

We also already have the full list of classes available at launch: gladiator, marauder, pugilist, lancer, archer, thaumaturge, conjurer, and arcanist.

We also have the full list of jobs available at launch: paladin, warrior, monk, dragoon, bard, black mage, white mage, summoner, and scholar.

For clarification purposes, both summoner and scholar specialize from the class arcanist. Your level comes from your base class. This means that if you level arcanist to level 50, you will have both scholar and summoner at level 50 as well. However, both jobs must be unlocked through separate quest lines which will also unlock their five unique abilities (meaning that you can have a level 50 arcanist, but if you've only done the quests for scholar, you won't be have any of the summoner-exclusive abilities until you complete the appropriate quests).