2nd Job Predictions

[Grey_Cain]

Check OP: Dark Knight

You're focusing on the wrong things in that list:

II: Leon joined with high Strength and Stamina and starts with a set of diamond equipment for armor.
III: Original NES, they had high Str/Agi with low Vit, but in the remake they had high Str/Vit and low Agi. In both versions, they could wear the second-highest defense armor set at end-game.
IV: Cecil as a Dark Knight has higher HP and defenses than Kain at the same tier.
X-2: "The Dark Knight dons heavy black and spiked battle armor."
XI: Wears heavy armor.
XII International: Ulahn (hybrid DRK/DRG) wears heavy armor.
Tactics: Gaffgarion (Dark Knight in the PS version), the Dark Knight job in the remake, and Argath (Death Knight but same abilities as Gaffgarion) all wear heavy armor and wield heavy shields.
Tactics Advance: NPC Grissom's job is Dark Knight although his abilities are the same as Paladin.
Crystal Chronicles: The original had a Dark Knight NPC wearing heavy armor, and in the prequel that NPC's heavy plate armor was equippable.
Four Heroes of Light: Dark Fencer, even though not a knight, is Strength primary, HP secondary.
Bravely Default: Not an FF, but close enough, and the job is high Str/Agi with HP as its third-highest stat. Also wears heavy armor.
Dimensions: Wears heavy armor.

I'll give you, especially with FFXI in there, that Heavy Armor does not necessarily make a tank. LNC/DRG already gets a set of mid-heavy armor that doesn't really do much for them, after all. But the image of a heavily-armored fighter is the image of a tank, and WAR supports this as its XI version was relegated to just another DPS while in XIV it's actually a tank.

Despite the mechanics, Dark Knight can also be a very qualified blood tank, especially with access to heavy armor and defensive cooldowns, and it could even be a LNC job! LNC already has the aforementioned tanky mid-heavy armor, a stun, a life drain ability, and a +damage/-defense ability, although WAR has most of those too and real heavy armor to boot.

In the first place, it's not any kind of a stretch to see DRK as a tank. Personally, I foresee LNC's next job as a tank, and if they decide that each class's jobs should provide a different role from their other jobs then I think we'll see DRK as a tank off of LNC.