Yes, indeed Neolionheart (almost typed Neonlionheart lawlzy), DRK wasn't a job very present in a lot of FF.
It's a bit of a "maybe we'll include in this game maybe not". It's a bit generic on what it can do because different FF had different ideas for DRK (only one thing in common: Sacrifice <insert something here> to buff <insert startus here>).

Maybe that's kind of why I like FFXI in the end.
Corsair is a new job in the FF universe I think. There are based-in-RL-luck jobs like lolLady Luck in FFX-2.. but the whole idea of Corsair was a very nice add.

I do think that the FFXI's Dark Knight is a very unique DRK, and essentially a very well built (in paper) job too. Maybe poorly executed, but well built.
I guess that's kind of why I really want to see updates and tweaks. It's a shame to just kick the "fuck it" button to this job.