You actually brought up a few points I hadn't thought about when I initially posted this, and I was going to edit into the post today, but I'll just post as a reply.
For the reasons behind my initial post, I believe that all of the tank job kits should be more or less "complete" by lv 70 (for both the leveling players enjoyment and for ultimate content as well)
with lv 71-80 adding traits that further empower their already existing kits. this would make each job feel more complete, while helping new players get used to their toolkits at an earlier level. i think this may be a more natural way to solve the problem of tanks not being up to par at lv 80 content.
For BW and Edge being moved earlier, they might not seem to be big changes, but I would suggest moving these just to make those middling dungeons a little easier for new DRK players. not everyone plays POTD, so they have to suffer with having those synced levels, and this makes the lv 28-38 dungeons a bit of a chore.
for Dark Missionary, It might be a little too overkill for HW, but I think if anything the 10% magic reduction isn't a whole lot when compared to how much stronger Divine Veil is at raidwide mitigation at that level. either way, my reasoning for this choice was that I had a convo with a friend of mine (he just started at shb) in which I asked him what he thinks DRK could use in their toolkit, and he suggested missionary because he noticed there is a lot of lv 58-76 content in which missionary could be useful, and that the hole in DRKs kit at lv 58 would be a nice place to have it. having it at lv 58 wouldn't hurt the lower end HW dungeons, and would allow DRKs to begin learning about raidwide magic mitigation at a much earlier stage in their gameplay.
As for Stalwart, I do think you're right about Stalwart being too strong. I initially thought it would be fine with its current power level only if abyssal drain was reintroduced as a mana spender, which is why I suggested it get a trait at lv 72 to bring it up to power, but I guess I should have elaborated on that. the current iteration of stalwart can definitely be reigned in like you suggested,
lv 40 would be something like 160 potency, 300 mana generation
lv 62 blackblood trait makes it generate 10 blood gauge
lv 72 enhanced stalwart would make it 600 mana generation/20 blood gauge
I just think stalwart is a neat tool and its animation is great, but it shouldn't be restricted to a lv 72 skill. not only do the other 3 tanks have their full aoe rotation by lv 40, but moving stalwart early would also help with the mana generation that DRK is lacking in its 1-70 kit. Pre-50, it only has Syphon and BW, and by lv 60 it only adds CnS (which is a measly 600). the problem imo is that all of these are single target, and it makes unleash feel somewhat weaker in comparison. by adding Stalwart in, I think that DRKs can get that hole in their kit patched up quite nicely. to further add in, I play a lot of synced content with friends, and I noticed that DRK feels somewhat squishier than PLD in the pre 60 content, and what better way to make up for that lack of defence than with a stronger offence, as DRK always did?