Refer back to the point of; " Ok then who cares, why waste the time to revert it then".
Meanwhile the complaints that are here rarely translate over for better or worse, although wanting to bring something back tends to work. Hello Scholar's Energy Drain.
If Cure I spamming wasn't griefing, if not using your role actions wasn't griefing, when somehow seeing the same thing 4+ time in a row after being explained time and time again doesn't somehow get across, when melee's refuse to AoE on groups of enemies, I'm not quite sure what else there is to it. I suppose you can throw in the odd RDM in early content where your tank stance wasn't available yet ripping aggro from you. Thankfully you already mention that in your post.
NA can barely handle markers let alone macros. Assuming you didn't get the people who turn chat off or tunnel vision of course. Not to mention communicating to the people who don't want to use those skills in the first place just leads to falling on deaf ears.
So you're ok with Dark Mind getting better, yet you also say removing DRK's "niche" would homogenize it further. Yeah, I want it to be better. This isn't even niche for the sake of being niche, you're just asking for a worse tank at that point. Might as well have PLD's "niche" of not being able to block magic back. Or how Berserk used to give Pacification as a "niche" thing that required Esuna. Or DRG's niche of dying easily to magical raidwides. Maybe even DRK's old Living Dead just to be the tank with the worst invuln for its standout "niche". Just mitigate all damage like a normal tank without any terrible downsides.
At that point one can spread out and figure out how to make it do good stuff in its own way. Again with Blood Price healing back 50% damage taken per hit, it wouldn't full heal but it'd be quite strong on slowing down the death of HP which combined with shields could make it purely devastating on top of the magical burst it offers. Lean into the MP management like usual but keep a general kit. We all have things like Rampart after all, and it was certainly "niche" when DRK's Shadow Wall had an extremely long cooldown for no reason compared to things like Sentinel or Vengeance. Were all tanks, but WAR is slow and steady with beefy health and fun cleaving, PLD has ranged magic and very good overall support, DRK is a magical burst who is a god with shielding, and GNB is a higher action tank that can burst out some nice damage while managing cartridges vs a standard gauge or MP and being a middle ground defensively.
That's a better route to go instead of keeping some terrible weaknesses for the sake of it.