To say that BRD is less useful inside of Abyssea is just silly... I've seen Ulhuadshi- along with dozens of other NMs that cast -ja or -ga IV magic, or things such as Gates of hades- lay down a full abyssite of merit MNK in one spell (Yes, Ulhuadshi can do 3.2k+ Stoneja under 10% HP with barstonra on) With carols, this makes all such NMs as dangerous as a lolibri in wajaom woodlands. BRD will take the headache out of EVERY SINGLE NM INSIDE ABYSSEA aside from Rani, Shinryu, and debatably Azdaja and Apademak
Not to mention there is absolutely no way to cap haste without a BRD, and in a DD party giving that much haste will out perform a 4th of 5th DD (assuming you have a WHM in the party) by far, depending on jobs/gear.
If you have 2 brds and are cycling them out, not that you would need to, you could probably be capping attack without berserk on several relevent NMs in scars/visions.
Corsair too would out perform a 4th or 5th DD in a party with NIN MNK THF DNC, because blitzer's roll is coolbeans on non-2handers. Samurai roll also has its place if it can knock a 2hander up a xhit. 4hit Ukon w/o sam in party (roll 11) Can you hear me?
For the other jobs that are debatably useless inside abyssea- DRK/WAR can do everything war can (Assuming you have a pitchfork from halloween) proc wise and more for slashing blue procs. Capped gear haste means faster stuns along with weapon bash for more stun capabilities in dangerous situations. Torcleaver is a force to be reckoned with too.
TL;DR: The point here is that most jobs if played well have a use, except PLD. If you enjoy playing it, go for it.
Except PLD.
Except PLD.