Job Balance is extremely iffy at the moment due to certain 'atma' (buffs inside abyssea) making critical hit weaponskills extremely strong and giving mages near-infinite MP. I'll give a rundown on how I perceive the current state of things.
Some explanations:
Empyrean Weaponskill: The current system for obtaining most good weapons is called "Trial of the Magians" (
see here). For each weapon type there are a couple of weapons (one strong one with some cool stuff which is reasonably difficult to get, and an easier no frills version with just the WS) which grant the user a special weaponskill. Some are pretty mediocre, others are extremely potent.
Atma: A buff system that only operates in abyssea. For each "lunar abyssite" one possesses, you can activate one atma effect. Currently two are obtainable, it is expected a third one will be with the upcoming heroes of abyssea. Atma are obtained from NMs (the droprate of which is greatly increased by performing certain elemental weaponskills to proc a "Red !!", or a couple of decent ones (at least for mages) can be synthesised upon completion of mission lines (nations, expansions, non abyssea add-ons).
If you're wondering how they change so much, for mages
look here, for melee DD the main culprit
is this. In the case of Atma of the Razed Ruin, no comparable atma exists which boosts non critical-hit weaponskills in a similar way, meaning jobs without a good critical hit weaponskill are shafted.
MAGES:
White Mage: Currently the only mage to get a cure beyond Cure IV, which means they are not only the primary healer job they are becoming the only viable one for hard fights. 450hp doesn't cut it anymore when people have 2-3k. Acceptable melee DD with hexa strike.
Red Mage: RDM always has been and still is a powerhouse, although it's not a great main healer these days. Fast Cast allows it to pump out nukes faster than other magic users, more than making up for smaller individual nukes, and the strong sword empyrean weaponskill actually makes it a somewhat respectable melee DD (lol).
Black Mage: Still useful for burning down groups of mobs and procing various spells on NMs to potentially increase droprates. Loses to RDM at damage purely because it lacks fastcast, but that doesn't mean it can't pack a wallop.
Scholar: Not getting Cure V has kind of put the nail in the coffin for healing, and infinite MP means the MP efficiency it used to have as an advantage on BLM is negated. Not great.
Summoner: I'm not really sure about SMN, I know atma buffs affect their pets which give them a nice boost but unless you're worried about hate or something silly like that other jobs are probably better.
Support:
Bard: Still as useful as ever for pumping melee DD over the top, it can even do semi-respectable damage with a dagger.
Corsair: Since its old main benefit (increased XP gain) doesn't work in abyssea it falls back to the other buffs it offers which are still strong. OK damage potential on the side.
Dancer: In the absence of a WHM they are a great healer, interestingly they have become a top tier DD (literally able to compete alongside monk and ninja) with recent improvements.
DD:
High Tier: Level these, they're awesome.
Warrior: Absolutely monstrous in every way. Amazing job traits, good crit WS (bread and butter Raging Rush is excellent, the greataxe empyrean WS is even better), good area effect WS (Using "Fell Cleave" no other job can burn down groups of mobs better) and ability to use nearly every type of weapon in the game to proc Red !!. Mathematically far and away the strongest DD and great utility too. Top tier.
Monk: While not quite as potent as warrior, it has better survivability (higher HP and counters that actually negate the hits you take). Excellent empyrean weaponskill and Razed Ruin atma makes Ascetic's Fury (the previously mediocre nyzul weaponskill) stronger than old staple Asuran Fists. Top tier.
Ninja: Now able to cap gear haste while also sporting a bucketload of dual wield equipment, NIN has come from behind to the top of the pile. Katana empyrean weaponskill is excellent, too and RR atma beefs Blade: Jin up nicely. Working with warrior together they can cover every weapon needed for Red !!. Top tier.
Mid tier: Jobs with a good Critical hit WS that are not on top but still strong.
DRG (several new jumps are good, drakesbane is even better with atma, but the empyrean WS for polearm is mediocre), THF (Treasure hunter is being buffed this update which will make them all the more desirable as well), Beastmaster (good new jugpets each update), Blue Mage (not sure about these, MP allows them to spam spells with abandon and spells unique to them are useful for possibly increasing drops)
Low Tier: Jobs without strong critical hit weaponskills or something else holding them back.
PUP: While Stringing Pummel is an excellent weaponskill (and stronger with RR atma), lack of offensive job abilities and a pet who will actually
reduce your overall damage if you spend time on manoeuvres to buff it up hurt it. It can't tank as well as monk either.
SAM: No useful critical hit weaponskills, including Great Katana empyrean, limits their damage potential inside abyssea. Outside abyssea with their empyrean weaponskill they're actually ok, but what matters outside abyssea these days? (Not much).
DRK: Best weaponskill dark knight has access to in abyssea? Rampage. Using axes, DRK's tertiary weapon (of which it hasn't been given access to any new ones with the level cap updates giving them terrible base damage) is the best way to be competitive. Given that DRK's job abilities aren't great to begin with and one of the best ones doesn't work with single handed weapons, both empyrean weaponskills it has access to are mediocre (relatively speaking) DRK is bottom of the barrel as far as DD go. On a positive note it's the only job beside warrior to gain access to Fell Cleave, although it lacks some of the tools that warrior has to make it shine.
RNG: Conventionally played ranger has never been great due to lack of an exponential buff like haste and low skills falling further away as the level cap increases makes combos like the Kraken club ranger less effective. DDing safely out of AoE's way isn't required much these days, either.
PLD: Technically speaking paladin is now less survivable than monk (less HP means more chance of being OHKO'd by a damaging move). Also, like every other job that isn't WHM it didn't get Cure V meaning its curing capacity is limited. While the sword empyrean weaponskill is handy, it doesn't have any offensive job traits to scrape it above mediocre damage output. Leave it at home.
I'm not saying "you must play this job" or "you mustn't play this job" (hell, my other job is DRK) but hopefully this is reasonably accurate and at least a little bit helpful. The level 90 update is hitting in a couple of days so I'll pass on any changes that occur. Questions, comments, criticisms, etc welcome. (Holy wall of text, batman!)