I mean tanks were unique once, with unique tankstances. Like paladin had more mitigation by default and warrior had no mitigation like that but more hitpoints and got more heal from healers by default. But SE stripped tanks of their identity basically.

I think what darkknight suffers from is that he should be a tank who leeches life from his enemies basically but the healing potency the job has on the attacks is really really low or well almost as much as other tanks (except paladin ofc) which makes it kinda strange. They could easily fix that by putting some selfheals on some of the attacks.

Darkknight really shines in raiding but idk 80% of the game is not raiding so it is kinda "stupid" to balance a job only around their performance in high end content while in Dungeons and all that they are just not as fun to play as like warrior who is basically an immortal aoe god who can clear the dungeon basically without your help.