They were originally going to introduce Samurai before Dark Knight but decided to not release two Easternish job classes so close together. Even though in many games the Dark Knight was never ever a tank class since it focused on sacrificing health to do absurd amounts of damage which we do not accurately have here. Instead they gave us a Tank that is all about sustainability.

Multi weapon users do exist in the form of Ninja's however a concern I've always had is outside of Crafters, Gatherers, and Paladins the Offhand slot is now never used by any other combat class and would do well to put something there to buff up a class's stats a bit more. And with Ninja's we can't even mix and match 1 of each of our short swords.

I mean the magic classes could be equipping magic daggers along with their staff's but they essentially have these 2 handed staffs that characters still hold in 1 hand.