The way I see it , at least in the case of BLM , is that youre not really a BLM , sure youre powerful and adept in the dark arts. But all along youre a THM being trained by black mages to complete some rituals and learn a few ancient spells to add to your arsenal.

Im assuming the same with bard , you dony suddenly become a bard , youre still an archer.

Im all for distinguishing jobs clearly from their base classes but that wont happen else theyd have to balance not 9 jobs but 17 in pve and pvp.