Oh, that.
But then half of the classes would need TWO pandora weapons anyways!
Well yes, but not necessarily.
You don't actually need to do job change until you want to advance to Master level, so you could go all the way to level 50 as your first class. For example, it's a lot more efficient to level up your Monk as an Acolyte (Ranged, Can self heal HP/SP) and your Beastmaster as an Archer (Ranged AOE). The other benefit to doing so as well, such as saving your job change skill reset until you really need it. Some skills you could take for level 1-50 grinding would not be useful for ML 1-30 grinding, which is where this may come into play. This is just my personal playstyle, I'm sure it's different from a lot of other people
But like Jhay said, Pandoras are only a nice bonus, you don't necessarily need them to grind quickly. My acolyte didn't get hers til level 29, and before that I was already tanking 10 mobs at a time in level 1 gear