I have less issues with the hoops DRK has to jump through and more with the fact that it isn't rewarded for it.
There are legitimate strengths that Dark Knight has, even things that no other tank has, and I'll even say I find the job inherently more interesting than FellCleave & FellCleave Accessories. The problem I have is that every strength it has comes with a draw back.
Like this:

TBN has a shorter CD than the other Tank Short Mits
But its also Weaker
And its the only one that can be a Damage loss, and no the game isn't really curated to see if TBN is even applicable in all content.
The existance of oblation doesn't really even the playing field.
Oh and you also just have no sustain, so you can very easily find yourself in scenarios where Dark Knight basically has no unique tools for tanking in certain content, and cant even restore the damage you'll take.

Dark Mind has the strongest effect of 20% Mitigation, AND 60s CD
Only against magic so theres a good chunk of content its not even applicable on


Now the existance of all 3 of Dark Mind, Oblation and TBN make dark pretty tanky in magic only fights, and only there. But not so much so that I think its a notable upside. Dark Knight will be pressing 3-4 mits to get by things, to other tank's 2 mits.
This isn't a bad thing, but the upsides of this rarely actually come into play, and on a tank thats already pretty high APM it can be chaotic.
I also think since the over-buff to Shake it off, its really questionable why Heart of Light or Dark Missionary are ALSO magic locked, I don't think it would break the game if this skill was more applicable to all content and not just specific mechanics of specific fights.


Basically all of this comes together to make a tank that is really frail and awkward in content the developers deliberately ignore when balancing the game. And with the addition of Criterion we can't even shrug that off anymore.