For the most part I agree with the OP. Pretty much touched on a number of abilities that are just a bit weak or weird feeling.

Though the Delirium change doesn't need to be anything more than add blunt resistance so we can put it up in place of a MNK so they can just DPS more, similar to how a WAR-NIN combo works now. Or as people have said before have it add some sort of other separate debuff effect to it like a %magic resistance down or something. It just needs something more to bring real utility.

Don't forget for Living Dead, it gets worse the stronger you get. More HP/VIT gear means healers will have to heal you more if it does proc.

I do agree the Dark Arts cost is huge, which wouldn't be an issue except DRK is MP starved and many of the abilities it buffs aren't that great when buffed. I honestly use it almost exclusively for a buffed Soul Eater now for the extra damage (not much healing since 80% of the time it seems when it's up in combo the healers already have me topped off). Some of the other abilities are just weak,

-Dark Dance buffed is not only worthless, but the evasion goes against DRK needing to get hit for some key abilities.
-Dark Passenger/Abyssal Drain are merely for trash pulls, worthless on most boss fights.
-Carve and Spit is up for debate, I personally don't think using all that MP for essentially 50 potency is worth it, and would rather use it to get MP back and use more Soul Eater. But I've not done the math so it could be better to DA it, but I imagine it's probably only slightly better.

Dark Mind is about the only other worthwhile ability to buff, but requires you're taking magic damage. Which is either difficult to know if what's hitting you is magical, or a lot of enemies are physical. So it's good, but situational.