Except that it isn't just Delirium being functionally identical. Several aspect of DRK's gameplay mirrors WAR in some way or another. Blood Weapon, for example, is essentially a weaker Infuriate. Through five GCDs, you're given 50 gauge and 3,000 MP except you have to play against a finicky server tick, potentially causing your fifth GCD to miss the effect. Warrior, on the other hand, simply pushes a single button. And because Inner Chaos is guaranteed to DCrit, they achieve similar damage output despite DRK having to work significantly harder.
Going further down the list Dark Missionary is a weaker Shake, both in the latter having a potential buff added and not having to play a guessing game on damage type. Abyssal Drain is laughably inferior to Nascent Flash in every aspect, having nearly four times the CD length in spite of being weaker.
You mention resource management yet... ShB DRK's iteration is the least resource intense the job has ever been. You essentially only pay attention to your MP under two thresholds: Is it above 9,000 or below 3,000? Anything in between doesn't matter outside burst windows. You ideally want to enter every buff window with roughly 9k and then let it build back up for TBN if necessary. As a result, this makes Dark Arts v2 incredibly passive... not unlike a certain other tank whose buff has become so easy to maintain you actively need to go out of your way for it to fall off. Keep in mind, everything I said only matters at an optimized level. For the vast majority of players, Edge of Shadow is little more than a spammable Upheaval. Which brings up an important point. Ever notice how Upheaval is rarely mentioned when identifying Warrior? That's because it's largely a forgettable skill you simply press. Fell Cleave defines the job. Edge of Shadow is similar; it's entirely forgettable. You'll simply press it, however due to the passive nature of Dark Arts, it lacks impact. Unfortunately, Dark Knight has no "Fell Cleave" to fall back on.
And that brings us to the only truly unique and identifying attribute DRK has: The Blackest Night. A cool ability, and undeniably better than any of its counterparts. Except being defined by one mitigation tool in a game centered almost entirely around damage is, well... underwhelming.
I have to disagree. Personally, I find it far more interesting weaving Dark Arts to buff Souleater and Carve & Spit while having to watch my MP knowing that should I let it drop, I'll lose Darkside compared to spamming Edge. The latter may be significantly stronger but it lacks intrigue and engagement. Dark Arts forces me to alternate combos and actively maintain a constantly draining resource. While it lacked in other aspects, primarily the fact you rarely wanted to buff Dark Mind due to it being a damage loss. The foundation gave Dark Knight an identity. Additionally, DRK was the only tank with active proc gameplay, further separating it from WAR and PLD in the Heavensward era. The similarity between tanks is a problem all around, however Dark Knight draws more attention because it had so much more diversity back in HW. In other words, it feels like we lost something with every iteration.
Which is a shame. She made a far more compelling argument than you did.