What could DRK have learned from FFXI?

[Absimiliard]

What? Cecil was a tank aka front line in heavy armor and the only one until he became a Paladin so yes darknight in IV was a tank.

Yes. The job with terrible magic defense, an extremely limited assortment of equippable items, and an ability that burns a significant percentage of its own health to deal damage is a tank. The only tank-like thing it had was high armor for that point in the game, and even that would start to fall behind if you for some reason decided to grind out levels for the few reasonably durable characters you get during Cecil's stint as a dark knight.