DRK was no more a debuff tank than WAR was a debuff tank in 3.0.
DRK has original Delirium which was 10% Int down and Scourge, a generic 500 potency DoT. WAR by comparison had the vastly superior 10% Damage Down, 10% Slash resist Down and Fracture, a generic 300 potency DoT.
DRk was simply a faster PLD with a more interesting MP management tank.
People like to cry about the changes from 4.0 to 5.0 and say that we had lost Dark Arts but frankly it had simply been renamed. Dark Arts was previously just a 140 potency oGCD in reality that had the roundabout way of simply placing the potency on the next GCD/oGCD. What do we have now? A 500 potency oGCD.
If you want to argue about Dark Arts as a concept of a buff that powered up their next action, then it really died in Stormblood when every action besides Carve and Spit simply gained 140 potency or had niche side effects that hardly mattered. (Enmity buff/AoE blind only effective in dungeons).
People like to whinge about 1 combo when 4.0 realistically only had DRK mainly use Soul Eater(*gasp* one combo!). 3.0 was not much more different where DRK pressed a 20 potency stronger button if they had no mana instead of Soul Eater. People like to whinge about Darkside as if it was inherently more interesting in Stormblood where it was a permanent buff that did virtually the same thing.
DRK hasn't fundamentally changed in it's oGCD/mana driven nature. It is very much a fast swinger heavy weapons user if you realize that DRK mashes oGCD swings like a madmen instead of receiving a temporary buff to spam Soul Eater 10% faster.
All people like to do is focus on Delirium(as if the previous one was any more interesting) and then slam the class for being a war clone on. One. Damn. Skill.
I frankly enjoy the new direction DRK is taking being heavy burst via oGCD(like it always has been) and the more controlled battery nature of its mana. I enjoy the big 500 potency swings inbetween the slashes rather than a 140 potency seizure they were previously doing. Other than PLD, every tank has a bland gcd cycle and that is attributed to the skill budget of the tanks various kits being put in oGCDS or Defensive Cooldowns. Old Blood Weapon isn't really interesting and would be counterproductive to current DRK with it's quad double weave bursts. I'd personally rather have more weaves and oGCDs to press for the feeling of speed rather than a bland 10% GCD buff to press Soul Eater faster.
Delirium can be more interesting but I'm not gonna be hung up and leave a class over one skill so /shrug.