What about creating an ACTUAL Dark Knight?

[Mahoukenshi]

You have a few things out of order here.

Dark Knight's 3rd appearance was in FFT(PS) (1997) as Gafgarion's exclusive job with 2 special attacks that dealt Dark element damage and recovered either HP or MP.

XI (2002) and the Advanced Job Dark Knight was released before X-2 (2003) and its Dark Knight.

There was also the the FF3 remake for Nintendo 3DS, where IIRC Dark Knight was only(?) a mid-tier job in the grand scale of things and had also the all-enemy hp-draining skill. It was recommended to use them with Bards for synergy during the parts the combo was valid.