So... am i missing something or is this the Dark Knights first appearance in a final fantasy game as a fully fledged tank?

There is the pseudo tank Cecil in IV but he still makes use of the Darkness ability which either deals aoe damage at the cost of HP or augments his physical attacks at the cost of HP (depends on version).

And then there is the Final Fantasy Dimensions version which is still heavily offensive based but has a provoke like ability as well.

Really, im not seeing any others on the wiki page, all other appearances are entirely offensive based.