Half of Ninja's kit is magic damage and you can think of Mudras as a roundabout way to "cast" with also letting you move about. Samurai also has "casts". You can't really make a melee job that has too many hard casts because many melee mechanics require a ton of movement. Samurai had 2s hard casts in SB and now they're 1.5s casts because 2s was too punishing.
Holy Knight's "Sword Skills" from FFT are reflected in PLD's skill set 80+ with Confeitor combo which has various aetherial swords raining down, not to mention Requiescat which is literally Hallowed Bolt/Lightning Stab.
Red Mage has the Mystic Knight archetype rolled in with its spellblade combo
Ninja has the Thief archetype rolled in with Mug
Warrior has the Berserker archetype rolled in with Berserk
Paladin has the Sword Saint/Divine Knight/Holy Knight archetype rolled in with Requiescat (Hallowed Bolt) and Divine Knight's various "crush" skills (Confiteor Combo)
Because of the above, we don't have room for Mystic Knight, Thief, Berserker, or Sword Saint jobs.
Moreover, we have enough swords:
Gunblade
Sword
Great Sword
Short Sword (many "Rogue Arms" are shortswords and gladiuses and not only knives and daggers)
Katana
Rapier
Enough sword jobs.
