Gladiator is the base class. You "attach" the paladin job class onto your gladiator (You still use a sword for gladiator, xp obtained as a paladin goes towards gladiator). In essence, paladin is an advanced form of gladiator. This is how it's always been. I haven't seen anything that says marauder will NOT be needed to do the quest to unlock paladin (So, even though gladiator is the base class, you still need some marauder levels to do the initial quest).