Only problem I have with the 2h sword idea is how many other theoretical jobs might line up with that weapon loadout (plus I personally find it unlikely a 2h sword class will be up anytime soon simply for thematic reasons).

Regarding Marauder I like how a lot of the design elements line up and from an aesthetic standpoint the attitudes of the marauders sort of bleeds into dark knights pretty well.

Regarding Gladiator I think the main push here is that you can set up some sort of dualit concept, the gladiator splits into the "light" class and the "dark class".

Having too many defensive cooldowns is a problem, but keep in mind the could always do to them what the did to the carbuncles for Scholar: Equipping the job crystal fundamentally changes how those abilities work.

I want a Blood Sword, I want the Ancient Blade, I want the Avenger, I want elemental swords, Hades Blade... I want a whole new line of Swords, not able to be wielded by the PLD.... maybe something like the exist swords stay GLD/PLD, and the new ones go GLD/DRK only...
That's probably really likely. I mean summoners and scholars don't share books either.