it's about realism Final Fantasy have some type of realism and rule they follow yes each game have it own rule and some even break rules made from other Final fantasy but the main point SE is getting with ffxiv is realism. Look how much work they did into the world to get realism each gear in the game you can tell what it made of.
Now how Realistic is to see a PLD without a cape or sword? some use hammer but really don't think they add hammer as a Wep in the game. How Realistic to see a Monk use a G.K?
Allow Jobs to use more wep if it fit with there job Monk= Hand to hand and staff RDM=Staff,sword Samurai= G.K,Polearm,bows PLD= Sword,Great Sword Warrior = Sword,Great Axe, one hand-axe. But don't allow everyone to use everything
Like i said before if unlocking a job is at level 30 class then i just level up 1 class to max level and each one to 30 and i have all jobs max level 50 without level up the class pass 30 even if am gimp with spell i still got enough to party with.