The reason elements don't do anything is cause in 1.0 people would take Tankx1 WHMx1 and then BLMx6 to basically everything cause they could exploit elemental weaknesses, all other jobs were basically obsolete. So for 2.0 they took out any form of elemental weaknesses and just made magic damage equal to physical.

Not saying I agree with this design choice, just telling you that's the way it is.