DRK changes that would make it really fun to play

[Archwizard]

in PvE, such a kit would be ridiculously hard to balance, dps wise.

I think you're misinterpreting the point I was trying to make.

I'm not saying "we need a 1:1 copy of the PVP Shadowbringer" because that would be ridiculous since, as you pointed out, PVP has an entirely different scope and context than PVE. A DRK dies in PVP and only he suffers; a DRK dies in PVE and your group just lost their tank. The PVP version of Shadowbringer is spammable as long as you have the resources, making it available significantly more often than you can use the accompanying TBN and allowing you to dump HP until you're at a critical level. Obviously, we can't afford something that high risk.

Rather, the point I was trying to make was focusing on the use of Dark Arts to subvert that cost, negating any such risk for a tank in PVE under normal circumstances. Presently, the existence of Dark Arts doesn't "reward" proper use of TBN, but rather refunds the cost TBN had in the first place in order to induce a "counterattack" narrative via Edge/Flood.

Were something like PVP Shadowbringer to be introduced in PVE, tuning knobs such as a cooldown and charges could be set in place to ensure that it's only used roughly as often as you can acquire Dark Arts, with the raw HP cost merely providing you an alternative to casting it when you don't get DA so that your mitigation and DPS won't negatively impact one another. Same flavor of Dark Arts we have now, but it actually rewards you rather than just refunding.
In an extreme (and however unlikely) case, you may even use such an HP cost as sort of a magic wand to charge up some of the other effects I previously listed, giving you a small measure of personal control over your HP as TouchandFeel noted we lack. I'm not trying to advocate this route specifically, I'm just noting the open possibility to make and connect such tools.

Overall though, the reason I brought it up at all was to highlight that DRK's history and flavor provide plenty of opportunities for creative tanking tools (especially with PLD intentionally being straightforward and WAR not having any thematic magic or gadgetry), which is part of what makes its current position so underwhelming.

There's also major problems with any tank that wants to be low on HP for any reason, since it literally runs counter to the healer role's modus operandi.

God if I don't know it from DRKs screaming at me to stop healing them 'cuz they popped LD at the top of a pull with two HoTs, an external DR and a barrier on them.
(Like, I don't know what you want me to do there, bud. I'm on SGE, if I sneeze too hard it heals you. Learn how to use your invuln.)

Of course, I'm also convinced the 6.1 LD buff was just a holdover for a future rework, since they did the same thing for skills like Acceleration or the entirety of MNK's kit last expansion before bigger reworks in EW. The literal layers of complication on it now (in lieu of just... removing the Doom timer) have that certain vibe, y'know?

Even beyond that, there's just the issue of how you'd balance the actual mitigation values contrasted to the other tanks. Since you either end up in a situation where DRK's mit is weaker than every other tanks 90% of the time and only equal if the DRK is at low HP to prevent its mitigation from being overpowered, resulting in a tank that is far more cumbersome to utilize in a group setting compared to just picking literally any other one, or you make their mits equal in 90% of situations to maintain parity with other tanks, but then make them OP when the DRK is at lower levels oh HP, resulting in DRK being wildly out of whack and a mess to balance since it would easily trivialize tougher mitigation checks or basically have infinite invulns with proper setup.

And I also suggested that a Macrocosmos-esque effect that charges up as you take damage would fit too, rather than just snapshotting while you pray you hit the mit before Bene goes off.
... And even that couldn't be any worse than Oblation.

The list I threw out wasn't comprehensive, nor end-all-be-all. At the least, it was my attempt to illustrate the versatility of the theme besides just "Dark Wave go brrrr"; at most, an effort to get creative juices flowing.

[Mikey_R]

Rather, the point I was trying to make was focusing on the use of Dark Arts to subvert that cost, negating any such risk for a tank in PVE under normal circumstances. Presently, the existence of Dark Arts doesn't "reward" proper use of TBN, but rather refunds the cost TBN had in the first place in order to induce a "counterattack" narrative via Edge/Flood.

That's the thing though, you don't want to reward the use of a defensive buff with more damage, otherwise the defensive will be used for offence and will feel bad if if absolutely had to save it to use it for an actual defensive purpose. You can just look to HW and, IIRC, SB PLD for an example. Sheltron/Bulwark were useful tools to get a Shield Swipe proc and were often used for the purpose. Sheltron even had MP regen attached to it in SB and, with how tight PLD's MP economy was then, you bet Sheltron was used to help restore MP so that you could get all 5 Holy Spirit casts in.

Rewarding defensive play with offence just does not work.

[Archwizard]

That's the thing though, you don't want to reward the use of a defensive buff with more damage

Rewarding defensive play with offence just does not work.

Have you met my friend, The Blackest Night? I think you two would hate each other.

[ForsakenRoe]

Have you met my friend, The Blackest Night? I think you two would hate each other.

TBN is damage neutral...? Like, yeh, the 'benefit' of a welltimed TBN is that you get the bonus of 'oh it didn't cost 500 potency', but many people have (quite rightly tbh) pointed out that this is not a bonus, this is a kick in the groin when you DON'T get the refund. Having damage gains attached to mit is as bad an idea as attaching damage to healing tools. Look at Assize or Earthly Star. We don't use em to heal, we use them for damage, and if healing happens to line up, that's just a bonus on top. Now look at Pneuma and Macrocosmos, they have the same potency as the filler spell they're replacing, so they're completely damage neutral. Unless you're in AOE, in which case they're a gain, but that's beside the point. Back to DRK we can see that in this regard, TBN's issue becomes clear. It's not the fact that you get a 'free Edge' when you use TBN, it's that there's a chance to 'lose an Edge' by MISusing the skill. That shouldn't be a thing. Just adding a side effect that says that you get the effect of Dark Arts when the TBN is broken or expires would fix the issue. You still 'lose out' on job effectiveness by mistiming TBN, but it's by having part of the barrier unused. It's not fun to suffer a 'punishment for mistiming the barrier' when you're progging, use TBN, and the boss autoattacks once and then starts casting a spell that interrupts it's autoattack cycle.

TBN doesn't 'reward use of defensive buff with more damage' unless you count 'you can move an extra Edge into raidbuffs'. It rewards use of defensive buff with 'you didn't get cucked for 500p' which is a much more apparent issue.

[Archwizard]

TBN is damage neutral...?

Yes. And what I suggested wouldn't affect damage at all -- the only reward I'm suggesting is a cost reduction that effectively increases survivability, which is no different from people arguing for it to HoT when the barrier breaks.
You're not locked out of using the DA spender if the barrier isn't broken in time, because you can still use it without DA and TBN doesn't eat the resources needed to cast it in the first place.

If you want me to get more specific with what I mean, here's an example to clarify:

* TBN no longer costs MP to activate, but it's on a 25 sec CD like other on-demands. A weaker version of TBN (Shadowskin?) is available at lower levels that has a lower potency barrier and doesn't give DA.
* Shadowbringer has a 30 sec CD and 2 charges, no MP cost but consumes 20% of HP when activated. A weaker version is available at the level TBN is introduced (Flood of Shadow?).
* DA reworked, now causes Shadowbringer/Flood to be cast without an HP cost, and up to two DA charges can be stored at once.
* Abyssal Drain replaces Flood of Darkness/Shadow as the AoE MP spender. Carve & Spit is upgraded to a cone attack with damage falloff on additional targets, and no longer shares a CD with Abyssal Drain.
* Edge of Darkness/Shadow now restores HP whenever it deals damage.

MP is used for draining attacks to heal you just like PLD's spells (which also helps recover from any Shadowbringer overspending), DA remains damage neutral because it's not on an MP cost or refund. You can choose to play conservatively, only using Shadowbringer as often as you have DA, or take calculated risks using the extra charge during burst (which you can quickly recover from with your MP spenders), and how well you thread that needle could become a point of skill for the job at high-end play.

And disclaimer, I want to make explicit here that I'm only defining this example to clarify what I mean, not as advocacy for a specific path the devs could or should take. I'm illustrating just one of many possibilities.

[Mikey_R]

* TBN no longer costs MP to activate, but it's on a 25 sec CD like other on-demands. A weaker version of TBN (Shadowskin?) is available at lower levels that has a lower potency barrier and doesn't give DA.
* Shadowbringer has a 30 sec CD and 2 charges, no MP cost but consumes 20% of HP when activated. A weaker version is available at the level TBN is introduced (Flood of Shadow?).
* DA reworked, now causes Shadowbringer/Flood to be cast without an HP cost, and up to two DA charges can be stored at once.

Let's just cut to the relevant bits.

You have made TBN an offensive action now. By giving you a free Shadowbringer you save your own HP but also the healing from healers and all you have to do is make sure you TBN every 30 seconds. What, you want to save it for the tank buster? But, if I delay it, I lose out on a free Shadowbringer. I want to pump out as much DPS as I can, without hindering everyone else. I don't want the healer to stop DPSing just so that they can help to heal that 20% HP I lost when I can get it for free. Even if I use Edge to mitigate the healing (depending on how many you need to heal yourself by 20%, let's assume 1), then technically, the Shadowbringer is not free, it has cost me 3000MP, maybe more if it requires more casts, and if I cannot supplement that healing requirement, it then falls onto the healer, so now you have punished them instead.

Whilst this might work thematically, please please think about how it would work in a fight. If I were to do this, what are the consequences of these actions. Is this choice going to negatively affect someone else.

Also, point to a healer that would like to see a tank's HP yoyo around as they use their kit.

[Archwizard]

You have made TBN an offensive action now. By giving you a free Shadowbringer you save your own HP but also the healing from healers and all you have to do is make sure you TBN every 30 seconds.

So what makes TBN an offensive action here is that you're using it... to save your HP. Seems legit.

Even if I use Edge to mitigate the healing (depending on how many you need to heal yourself by 20%, let's assume 1), then technically, the Shadowbringer is not free, it has cost me 3000MP

And TBN already does every time you use it.
You literally are trying to have it both ways, each time you've spoken on this you've taken shots so broad they hit the existing TBN in the crossfire.

And, I cannot stress enough, I'm not saying "It'll be fine if they do exactly this." It's just a demonstration. I'm not gonna argue the specifics on a made-up example.

Also, point to a healer that would like to see a tank's HP yoyo around as they use their kit.

That's part and parcel with playing alongside any tank besides Paladin, at least since 6.1.
Warriors have lighter mitigation than other tanks but make up for it with self-healing. When a WAR takes big hits, we just shrug and say "Oh, he'll be fine." They're also... kind of the favorite tank right now.
When Gunbreaker uses their invuln, after the momentary heart attack, we shrug and throw a lazy HoT on them.
When Dark Knights want to use their invuln now, they pretty much stop using any mitigations and sink like a stone anyway. Sucks, but we're getting used to that.

So if you told me that DRK was able to self-heal from that occasional 20% hit due to supplemental changes to its kit, on top of it having above-average mitigation, and that I'd only have to panic if they did something incredibly dumb, I'd shrug like I would with WAR.
Is it a bit of a pitfall set for inexperienced players? Maybe, but only as much as being able to hardcast 5 second-long spells on RDM, or not being locked out of opposite element spells on BLM, or... half of the other jobs available. Knowing how to manage your own resources is part of mastering each job.