The Blackest Night gets too much praise for what it does on paper, but in practice, it's way less fun to even try and get the shield to break because of it being DPS neutral on break and DPS loss on falloff, and making it be a DPS gain on break and DPS neutral on falloff.
Stormblood TBN was DPS gain due to generating 50 blood gauge, assuming you didn't cap on it of course, and DRK are capping blood gauge way too much to where they can't get Bloodspillers out fast enough in Shadowbringers, and Living Shadow doesn't help due to how long the recast timer is which also makes it weaker in practice.
Speaking of Living Shadow, just make it be an upgrade of Darkside since it is technically our Darkside that we still have to maintain and make sure we get 15-30% damage up for Darkside being active, because 10% isn't even noticeable... Also make Souleater combo maintain Darkside/Living Shadow
Bringing back Dark Arts and making so you have to spend 50 blood gauge for 20 seconds while boosting attack potencies by 140, and it upgrades into Delirium, because Delirium needs to be improved upon it's Stormblood version by restoring HP and MP for 50 blood gauge while removing blood gauge costs for other things for 20 seconds for and increases potencies by 350, instead of the current "Inner Release but worse" because spamming 5 Bloodspillers is not fun.
Sole Survivor was just fine in patch 4.3(if I remember all of those DRK buffs from then correctly).
Dark Passenger shouldn't have been removed from the beginning and just reworked as a cone AoE and the beginning of a burst combo involving Flood of Darkness/Shadow, similar to how GNB and RDM have a burst combo, albeit DRK would have a burst combo for single target and a burst combo AoE and Quietus could have been the middle button of the AoE burst combo though it would mostly be a trait at when you get Quietus.
Salted Earth needs to do more damage and/or last longer for it's long recast timer because it just sucks...
Abyssal Drain, why is it a oGCD and not part of a standard 1-2-3 AoE combo like how DRGs have one? I am perfectly okay with reworking Unleash and Stalwart Soul as target AoEs and nerfing the cure potency on Abyssal Drain to like 50 per target
Carve and Spit, I like the animation but oGCD makes it meh for me. A trait where it is the combo ender for the single target burst combo, making Bloodspiller the middle button, and Edge of Darkness/Shadow is the combo starter for said burst combo.
Reworking the blood gauge for burst combos to make them 140 to 350 potency stronger shouldn't be that hard...
Reworking Dark Mind to where it has 100% parry rate so that it handle physical attacks better because DRK needs it badly...
Blood Weapon needs to restore HP AND MP whenever you inflict damage AND you get 15% faster GCD and Auto Attacks and you need to maintain Blood Weapon with a gauge builder combo A.K.A Bring back Power Slash combo.