1, new basic combo / to be honest, I truly hate the idea of a action becomes a complete different action through a trait upgrade. these kinds of lazy and lousy effort-skip designs that the devs use in the combat systems is one of the reasons why FFXIV's lost RGP elements and lost sense of combat being fun will never come back.
2, Edge and Flood of Darkness/Shadow / my own thoughts would also be a MP cost reduction(to 2500 or 2000), personally.. I would reduce their DarkSide extension effect down to 15 seconds, and I would put their oGCD on CD(no more spam), and then make other oGCDs also grant DarkSide effect and/or only extend DarkSide's duration, still by only 15 seconds.
3, Blood Weapon concern / "only effects WeaponSkills" is a bad idea, in my opinion, just to start. I could agree with a CD reduction, but I am not certain of what CD would be a good rotation mark... 40 seconds is not.. too of a bad idea?.. in the sense of 2.40 GCD x 31 = 38.4 seconds / 2.40 GCD x 32 = 40.8 ...so like, clean weave Blood Weapon between every 31-32 GCDs? while the reason why I am not certain that this is a good idea, is because CDs dictate rotation, and so every other CD would need be able to coincide with or nor over-lap with a Blood Weapon every 40 seconds and 31-32 GCDs. additionally, I do not agree so much with the sort-of common "grants stacks" opinion. this idea was brought up to fix Blood Weapon's 5th GCD issue, but it would be more of ease to just increase its duration to 11 seconds.
4, to address the Dread Spikes idea / I do not so much like the idea of Dark Knight gets.. another.. Warrior copy-and-paste ability. here is a alternative idea. what if "Dread Spikes" is more like The Blackest Night?, in the sense of being a magic barrier, and any attacks that strike the barrier is what triggers the counter. then just give it a "if broken" bonus, much lower CD and a MP cost. at least then.. the ability would be Dark Knight unique and not a Warrior copy.
5, Stalwart Soul concern / Stalwart Soul is already bad enough, and taking away its MP restore, to lock it behind The Blackest Night being Broken to grant not-Dark-Arts "Dark Arts", and then spend that effect on Stalwart Soul, instead of some where else more of use, is quite a bad idea, in my opinion.
6, about Scourge / I can, how Ever, agree with the return of Scourge and its DoT.
7, ...Living Dead... / I have posted my full thoughts on this pitiful ability in other threads, that were titled to be in specific about Living Dead, concerns about Living Dead, and Living Dead ideas... you can just check out my post in those threads.
8, about Salted Earth / and as for a all-around buff to Salted Earth, I can agree with that.
9, about The Blackest Night / your idea for it is not bad, but I will say this. the way that The Blackest Night has any connection at all to Dark Knight's damage potential is lousy and stupid design. The Blackest Knight should have no connection or relation to damage output, and should be a pure defensive ability, while the "if broken" nonsense should be a defensive bonus, HP-related bonus, utility bonus, or even just some sort of a new effect; just.. aught that is not damage-related.
10, about BloodSpiller and Quietus / your ideas for those two is not bad, at least. I can agree with at least giving them additional effects.
11, about Dark Mind and Dark Missionary / I can agree with the CD reductions, but I am not as certain about to weaken Dark Mind's effect... is down to 20% fair, or 25% instead?
12, about Living Shadow / pitiful excuse of a lousy and turned out to be lame ability, that is just a mere glorified DoT. it needs.. a lot. it needs to be so much more.
13, about current Delirium / should just be thrown in a fire, burned to ashes, and never return, rather than improved. this worse-than-Inner Release Inner Release knock-off is a poor excuse of a ability. Instead, either HW Delirium or SB Delirium should return, or Delirium is given a new effect that at least fits with the definition of the word "Delirium".