No, all jobs are not equall to eachother in damage. But that's not the point
All jobs are DIFFERENT, and they are different in dealing damage. If a THF did equall damage to a MNK, it would be extremely overpowered, for the simple fact that THF concentrate on hate management. It can put hate on someone else etc. This is something a MNK can't do as efficiently. And that is where THF shine.
All jobs have different jobs in the game. That's why they call them jobs. If all would deal the exact same damage, they would just call them the same job.
DRG deal damage though themselves and through their pet. Its a pet job, and without their pet, their damage would be a lot worse. DRG, too, focus on hate management, that's why DRG and THF are a good combination, and they can also make Light together.
DRK deal good damage. They specializes in Scythe weapons. Slow attack speed, high damage. They can also use Absorb spells to strenghten their own weaponskills and damage, while decreasing the mob's ability in a certain area. They can also absorb TP in order to get higher TP. They can also drain the mob in order to get MP back and damage the enemy.
PLD tank through taking hits, and curing themselves and party members. They are there to protect their members from taking damage, by taking damage themselves.
All jobs have different situations where they shine. DRG does piercing damage, and have Dragon Killer, making them effective against mobs weak to piercing etc. THF works good against these mobs too.
MNK, on the other hand, deals bash damage. They are PURE DD's, in that they don't have any job besides dealing damage and curing themselves for when they get hate. This, offcourse, make MNK's very effective against things weak to bash damage, and slightly worse against things strong to it, like beetles and crabs.
WAR, on th eother hand, have 2 roles. They can either be tank, or DD. They can also wield most weapons. This makes them excellent DD's and passable tanks with the right gear.
NIN was originally supposed to be a DD job. And their damage have always been supposed to come though speed. With faster attackign speed, they will do more damage. That's why they get Dual Wield, because their damage comes from speed. They can also deal additional damage through magic and ranged attacks. The player based turned this around, though, and made them tanks. They still concentrate on speed, though.
SAM's, on the other hand, focus on TP and weaponskills. They can open and close pretty much any skillchain in the game, making them good skillchain partners with all jobs.
RNG's deal damage through ranged attack. They shoot at things, simple as that. They turn gil in to damage. They are 1 of 3 pure DD jobs. One can say they are a mix of MNK and BLM. BLM focus on burst damage, MNK focus on dps. If MNK is the far right, and BLM the far left, RNG is in the middle.
BLU's deal damage through spells, very much like BLM. However, BLU's are the most adaptable jobs in the game. They can either enfeeble the enemy, play melee DD, mage DD, tank, or healer. They can do all of them well, although not as well as jobs concentrating on that specific job.
WHMes are the healers. They heal stuff.
RDMes focus on increasing exp/hr by reducing downtime. This is their job.
BLMes focus on burst damage. They have close to none dps damage. Their cat single-hit high-damage spells for damage.
BRD are pure supporters. Their focus is to increase exp/hr by decreasing the time it takes to kill a mob, by increasing the other job's damage. They can also help slightly reduce downtime by increasing the MP reserves.
COR's are a combination between RNG and BRD. They can deal damage, but not as good as a RNG. They can also buff other jobs, but not aswell as a BRD. Their buffs are random, and thus, the overall efficiency of their buffs will be lower then that of a BRD.
SMN is yet another pet job. The difference is that their damage comes purely from their pets. SMN is a mix between PUP, DRG and BST, in that SMN can both play well in parties, and solo, although not as well as DRG and BST in their particular roles.
BST focus on pets, too. Theyr are excellent soloers, and can play excellent in parties if they are just given the chance. Just like DRG, they need their pets in order to deal good damage. Although I do admit they can deal good damage in merit parties with the right set up
PUP also deal damage through their pets. They can make their pet focus on either piercing damage, burst magic damage, or, I believe, slashing damage? This makes them able to adapt to the situation. Most PUPs just pure suck though, as they believe the main damage comes from themselves rather then their pet.
Either way, no job is identicall to one another. They all have different roles and jobs. This is why you'll see DRG's deal slightly less damage then a MNK. They are ment to. They are not a pure DD job like MNK is. This would be almost like saying RDMes suck because they can't deal as much damage as a BLM. They have 2 completely different roles, although DRG's role is still rather similar to MNK, in that they both deal damage, only through different means.
In order to play your job good, you need to figure out what your role in a party is. You can't go out and say "Oh, I'm a DD!". If you do that, you won't be able to strenghten your strenghts, and counter your weaknesses. Doing that is just stupid, and makes you look like a fool. No job is identicall to one another, and comparing a MNK to a THF or DRG is just pure stupidity.
