I figure since I'm being quoted directly as a supporter of Oblation, I should at least offer my perspective on the skill, and my affinity torwards it. Kabooa has taken the time to give some of the stats of Oblation itself, so I'll focus on it from a design standpoint instead.
Going to preface this with: I do not think Oblation is "good". I think it is adequate at best, certainly interesting, and probably deserves buffs.
To start with, I do not view Oblation strictly as a TBN+, although I have no doubt it was initially designed that way. While combined with TBN, it is quite comparable on busters, and falls behind afterwards due to a lack of recovery post hit that the 10% mitigation is not enough for.
But the thing that makes Oblation interesting is that it's not beholden to the same "restrictions" as the other short term cooldowns are. When you are shielding someone with your mitigation on WAR/DRK/GNB, do they REALLY need all of the effects of their respective cooldowns? Or is all of that healing going into overheal? Is that short term mitigation bump really making the difference between life and death? Naturally, the answer varies depending not only on the encounter, but on the situation in that exact moment of activation, both on the person giving the buff and the person receiving it.
Oblation at it's core emphasizes what I truly appreciate about Dark Knight post-Shadowbringers. And that is flexibility in the kit. While Oblation does not do any one thing very well, it does everything adequately. Rather than viewing Oblation as the second part of a decoupled TBN trait, I instead view it as a personal version of HW Reprisal, without the damage, on a stack system. and shorter duration. Let me lay out a few test scenarios in fights we have seen previously where I think Oblation has potential value.
Any fight that features a heavy prey damage on a DPS/Healer (A12S Blazing Scourges, O12S HW, E11S lightning tether)
While I realize many DPS have the ability to self mitigate quite well (MNK, RPR), I still think it is a tank's job to support the team as best as possible with mitigation. I bring up those three fights because all of those fights have prey markers that are subsequently followed up by, or happen at the same time as heavy tank damage through a buster or sustained auto attacks. This is why the 2 stack system is so interesting to me, because it allows the DRK to make choices without having tradeoffs. A GNB who throws their HoC on the DPS will do more than equivalent amounts of mitigation as compared to a TBN+Oblation, but their HoC is no longer usable for their own, or their co-tanks following damage. Oblation leverages this quite well, with giving minor mitigation if needed on the DPS, while still having the TBN and the 2nd stack for personal/co-usage. This is similar to what PLD can do with Holy Sheltron + Intervention, but the caveat is that both those skills are quite heavy investments, while Oblation isn't. It's kinda just there, while TBN remains free as an option for more heavy lifting if required.
Any fight that features either burst or sustained double tank damage. (TEA, E8S, P3?)
I would've killed to have a mitigation like Oblation on Living Liquid, CC/BJ, or Nael+Twin. Those are stressful heal environments in progression, and taking a few thousand damage off each auto attack for both tanks, even for ten seconds, give a bit a breathing room in what are somewhat hectic situations. It doesn't even need to be both tanks either, a GNB in Nael + Twin for example has a competitive edge over DRK's naturally because Dark Mind is only good for Megaflare. But if Oblation was in that fight, it would serve as a great alternative to Camouflage for the DRK personally, and whenever Nael would do quotes and Twin would attack only one tank during a heavy twister movement, DRKs could support whoever the Twin tank would be at the time, WITHOUT compromising their major mitigation in TBN for following tankbusters. On top of just giving both tanks a 10% if cooldowns were more appropriate for said auto attack damage.
It's a verdict weighing all of your eggs in one basket (non-DRK tanks) vs the option to spread out your eggs amongst the same or different targets depending on the scenario (DRK).
Trying to get a DA proc for raid buffs? TBN is enough.
TBN is too much, and won't break? (ie: kitchensinking cotank + helpful heals/DPS, or minor raidwide) Oblation on it's own to assist, assuming it's free and multiple stacks will not be needed in the next 60 seconds.
Heavy damage on a friend? TBN + Oblation.
Heavy damage on a friend AND another target? TBN + Oblation X2.
Heavy damage on a friend, another friend, a 3rd friend AND yourself? Like, split stack markers? Dark Missionary for the team, TBN 1st, Oblation 2nd, Oblation 3rd, and personal mitigations for yourself.
Kitchensinking? Add Oblation on top, it's free, pretty much.
Someone going into a raidwide like Akh Morn with a vuln or low HP? Just Oblation them to negate the vuln entirely, add the TBN on top if death is likely otherwise. (this will be relevant in P3S and P4S, I'm sure.)
Sustained auto attack damage? Light mitigation from your co-tank, and supplement it with 2 Oblations spread out over twenty seconds, try to catch a raidwide if possible.
And more. The argument I have is that ALL of the above can be mixed and matched with DRK's current kit all on ONE skill. In a game where we constantly invuln and dump our entire kits on a single buster, having something that encourages intelligent usage like this is a breath of fresh air, and I want to see the skill have more support.
There's serious potential for such a flexible mitigation. However, it's too weak. The cooldown is simply too long to be just a personal 10%, and it's underwhelming in dungeon content with such a low percentage. Now don't get me wrong, a 10% is good, Reprisal is still a great role action! Imagine all the Morn Afahs or late-phase Akh Morns you would've died to without that -10% damage from the boss? Sometimes, people just need a little extra. I am usually loathe to make suggestions, but to truly have parity with other tanks, and to make it a compelling, meaningful cooldown in all content at a surface level without this amount of theorycrafting about some nebulous "potential" the skill might have, Oblation should either be able to be used more often by reducing the cooldown down to 40/45 seconds for more usages, or it's mitigation straight-up doubled to 20% to be more impactful when it is used, or the duration doubled to 20 seconds to encourage spreading it out.
Hopefully that makes my thoughts on it more clear. I just love having more options, and more ways to help. I love defensive optimization, and Oblation feels like it was made for someone like me.
But it needs just a little bit more to push it over the finish line. At least it looks really cool.