Lorewise strongest job imo is the BLM . Not only do they draw their power from the Aether like the SMN's and WHM's but they also draw from the Void itself.

SMN's have a more controlled version of using the aether and are more akin to becoming primals in taking on aspects of the Eidolon they are summoning.

WHM's destroyed Ampdapor in doing battle with the BLM's for fear of BLM power because it was unrestrained and it since it being so powerful could actually destroy not only the world but the user if used incorrectly. Besides the Elementals hid the power of white magic from the world and only gave its secrets to a few but BLM's are not governed by the Elementals and so can not be contained.