Occult Acumen provide you TP each time you nuke with elemental magic (based on MP cost)
https://www.bg-wiki.com/ffxi/Occult_Acumen
like this:
With a decent "Occult Acumen" equipment, you can exceed 1k+ TP with "impact", which allows you for example to do skillchains by yourself like this:
Keep in mind though that this kind of skillchain only works on low level monsters that don't have much evasion. It is therefore an occasional use.
With caped fast cast and skill, you can expect land T6 T5 and T2 on each Magic Burst windows.
But keep in mind that black mages have been nerves, with the right buffs(especially the magical defense down "Malaise" of GEO (also nerfed) and good buff from COR) you can easily reach 100KDMG cap with a T4, which makes T5 and T6 or Death totally useless.
The black mages also encouter and terrible nerf if 2 black mages nukes at the same time, contrary to the other DD... thank SE... (you can find a test video on my chanel)