Mira, the issue is that in XIV they are Weapon Classes, Not Classes like you see in WoW or other games. (Hunter etc)

Gladiator litterally means Sword User in Latin, and in Japanese the same "Sword User". It is not a Paladin, a warrior or a dark knight. But it can be all three if you give it the right skills. As a "Class of Weapons" Gladiator is Swords and all of their uses, both offensive and defensive.