Seeing how for Dark Knight most people ( 90%!!! ) ask for either a mini rework or a full rework, here are some ideas for the tank problem child:

->Dark Mind grants 10% damage. At level 82, upgrades to Oblation, granting an additional 20% magic damage mitigation.

->Dark Missionary should be obtained at level 66.

->Carve and Spit / Abyssal Drain moved to be GCDs with 20 sec CDs.

->Bloodspiller combos into 2 more actions, part of a combo, each action costing 15 blood.

->Living Shadow increases Darkside's damage bonus to 25% for 20 seconds. Fray merges with you giving you an enshroud like effect but suited to DRK fantasy.

->Delirium grants the Delirium buff for 10 seconds. During this time Darkside cannot be obtained from Edge/Flood of Shadow, they instead increase the bloodgauge by 20!

->Quietus removed. Bloodspiller combo can have AoE fall-off.

->To replace Quietus and Dark Mind merged into Oblation you can gain Blood price and Sole Survivor.

->Blood price: When around more than 2 enemies, getting hit increases the Bloodgauge. Should be obtained in Stormblood.

->Sole Survivor: Marks target for execution. If target is killed, gain HP and MP. If target survives, gain only HP. Should be obtained in Endwalker for sustain purposes.

->Salted earth gives a regeneration effect while standing inside it. Salt and Darkness heals the DRK instantly.

Idea of mini rework:
Minimize the use of EoS/FoS outside Delirium, but make sure you keep Darkside up.
Maximize the use of EoS/FoS inside Delirium to increase the bloodgauge.
Use the bloodgauge specifically to use the Bloodspiller combo as many times as possible under Living Shadow.
Play around with TBN's Dark Arts!
More GCDs.
Merge similar defensive CDs for easier weaving of defenses, add identity in the defensive / utility kit, solidify dungeon sustain.
Add more intensity to downtime periods: C&S being 20 seconds and managing Darkside more carefully.
Distance DRK's gameplay from WAR.