you bring a lot of interesting points about the HW/STB DRK kits being disjointed, but at the same time you are dismissing valid complaints about the SHB DRK kit being disjointed, which has been a topic of major criticism and concern. are you suggesting you have absolutely NO problems with Salted Earth being nerfed as well as losing blood generation which connected it to our kit? Abyssal Drain losing its mana cost and being placed on a long cooldown rather than being changed to be stronger in single target? Quietus/BS being reduced to spam rather than well timed resource generation skills? are you suggesting that the ONLY thing that needs to be addressed for DRK is Living Dead, and not the lack of impact that a lot of the abilities have besides muh stronk tbn?
I might be in the minority here, but I actually think that the STB version of DRK was superior to the HW version due to a few key aspects, such as having a more dynamic resource management playstyle with its mana and blood interactions, and the overall streamlining of the kit with regards to how mana and blood worked with your skills. losing some of those DOTs and the fun MT revenge mechanics did hurt, but I believe what we gained from STB far outweighed those losses, especially because we got to keep almost all of the DRK core abilities, like DA, AD, SE, DP, and BP.
while you are correct that a lot of the more hardcore playerbase realised that spending DA on defencive buffs was a DPS loss, you're also forgetting that a lot of the more casual to midcore level players utilised those in their daily activities, where the environment is a lot more hectic than in organised pugs/parties in which you can rely on timed heals to make up for the damage. a lot of times in leveling or roulette content, spending mana on defencive buffs could mean the difference between living or dying since not every healer has immediate responses to incoming damage. plus, you're forgetting the most important aspect.. we had branching decisions we could make (whether they be """good""" or """bad""") which was one of the hallmarks of the playstyle that differentiated it from PLDs stricter rotation and WARs GCD based playstyle. this made DRK objectively unique in terms of gameplay, and made it feel fun to engage with the kit in terms of job fantasy.
as for your comment on how "all other jobs have changed", it's not hard to see that from certain perspectives, some jobs seem to have regressed in SHB, and that others seem to have stagnated in EW. did PLD really need MORE finishers, especially ones that combo off confiteor of all things, rather than fixing sheltrons cost and duration (especially at lower levels)? did DRG need ANOTHER AOE as opposed to a way to ramp up their eyes or a way to refresh to disembowl like how SAM does? did MCH really deserve nothing but a chainsaw and shotgun? did BRD deserve to have its procs and party buffs removed in favour of ... whatever they got? did SCH deserve to get ignored and told there wasn't much to change, despite almost 2 years of criticism from SCH players? don't even get me started on jobs that regressed in EW... rip DNC, NIN, and SMN mains of old. titan egi will be gone, but never forgotten.
the main problem I see with your issue of invulns and their impact is not DRKs fault, but rather the fault of the devs refusing to hire more employees to fix the spaghetti code, which is why battle content is designed the way it is. MY problem with DRK, besides its atrocious leveling kit, is that disjointedness between its job fantasy and the bone dry gameplay that in no way complements the job fantasy. and the biggest problem I feel is plaguing this game, is the increasing movement away from the more "technical gameplay" jobs with unique XIV twists on them, and that said jobs keep getting dumbed down in gameplay for the sake of "muh traditional FF version"
sure, by all means go ahead and buff Living Dead, but without fixing that disjointed feeling, the job will still boil down to spamming all mana in burst window, spamming 1-2-3 for 60 seconds. but now you get peppered earth and a new flood follow up!
"there wasn't much we could really do with DRK"