Wait... why? O.o
This is an excellent point that I haven't even considered. TBN+DM renders DADM pretty much obsolete right now, so the DA effect of that ability is pretty undertuned. Honestly after reading this I kinda wish they'd just redesign the ability entirely. I'm not a fan of the raidwide mitigation component suggestion simply because it doesn't fix either of the problems that I see with DRK right now; its DPS and personal mitigation. I don't really have a justification for it, I admit, but I just feel like what DRK needs isn't bordering-on-PLD-levels of utility. It needs more damage to make up for its lower utility, and it needs some sort of addition or buff to its defensive kit. Basically, in fights where DM isn't used, I find it... jarring... to rely solely on TBN for a full minute or more in between Rampart/Shadow Wall casts. I wish that the ability was not so lopsided, its powerful and that's great, but I would rather they increase its recast time a bit and redistribute that power into another CD to give us more options. Getting the most out of TBN requires a DRK to know a boss's rotation down to the last auto-attack which I honestly find a little silly, and an artificial illusion of depth/difficulty/complexity.
Anyway. I given that they've now established TBN as the standard for mitigation-to-mana, it seems like they need to add something equally powerful to DM in order to make it relevant. Since TBN basically defines DRK mitigation now, we're a shield tank, so my gut tells me DADM should just be DM with a TBN effect tacked on, that lasts longer but doesn't grant Blood. Powerful, sure, but for a DPS loss and a longer cooldown... idk.
Like I said in the OP, I feel like Shadow Wall was tuned in such a way to make up for the high uptime of Reprisal's personal mitigation. We're missing that -10% now. Sure we have TBN, but now PLD can block magic, WAR has Rampart... idk. Without the DD+Reprisal Combo, Shadow Wall feels extremely weak. It also occupies such a strange spot in our cooldown suite. Not all fights will be like Susano, surely, but in that particular fight I had Rampart+TBN for every buster and would look at Shadow Wall and be like... what do I do with this? Eventually I started using SW instead of Rampart every other TB, but then for certain rotations I'd have Rampart and other's I wouldn't. Again, the term lop-sided comes to mind.
LD... for once I can't really empathize. I'm fully aware of LD's shortcomings, but for whatever reason, in my personal experience it has never left me wanting. I think I'm less focused on it because it is an invuln and I'm more concerned about our high-uptime (or lack thereof) cooldowns.
I think maybe I wasn't clear. My intention wasn't to make BP see more use it was just to add something to our kit that gives us an additional mitigation option at the cost of some DPS (being locked behind Grit), since all of the other tanks have something like this (Clemency, IB, Equil, even PoA). They all have that option to supplement their core cooldown suite with something extra if they are willing to sacrifice some damage, resources needed for damage, or go into tank stance. DRK doesn't really have that. It has 4 innate cooldowns and that's it. Both WAR and PLD have a powerful self heal and an extra albeit DPS inefficient mitigation tool.
This suggestion makes my heart sink to be honest. What Souleater's heal needs is power, not accessibility. And even then, its locked behind a combo so its rarely possible to time it for when you need it regardless of how much it heals. Many is the time on WAR for instance where I have popped the absolute bare minimum mitigation that I would require to survive (Thrill alone, even Foresight back in the day) and just Equil'ed myself right back up to a safe HP level. No biggie. I find it really cheap that we cannot do this. And if we could heal ourselves for a meaningful portion of our HP as opposed to having what basically amounts to a slow, combo locked regen that mostly just contributes to overhealing, it'd go a decent way towards alleviating your previous concerns about LD.
My suggestions for DP where merely an example of a way to buff our DPS. I'm hard pressed to find someone that disagrees with the fact that having both less utility AND lower DPS than a PLD is textbook feelsbadman, and honestly since they aren't likely to add meaningful raid utility to either DRK or WAR post expac, the most logical thing to suggest seems to be DPS buffs. And I mean its just ridiculous from a thematic/lore standpoint. Why sacrifice a shield for a two-handed sword that deals less damage than a 1-hander? Why would 2-handed swords even exist in the game's universe from a technological standpoint? "Here's this two-handed, heavy sword that requires you to forego a shield, and yet you will take longer to kill monsters with it." Who would buy that? DRK should deal more damage than PLD. Everything else about PLD is better, but DRK has a big sword, so the most logical edge for it to have over PLD is DPS. Perhaps a more creative mind than me will have a better suggestion, but in terms of what the devs are realistically likely to add and suggestions they'll realistically respond to, a simple re-working of costs/potencies/percentages usually comes before adding whole new abilities/affects.