Enough is enough

[Sir-Meliodas]

But in FFXIV that is what is going on, there is a ladder system that rewards you for going with more difficult tanks.
The idea of the Dark Knight is that you have to use abilities in such a way to optimize your tanking ability. (You have to strike an equilibrium with the conflicting abilities (that was probably how the dark knight was designed)).
Living Dead is not optimal but it can work ( benediction and the fact that you can still take damage in LD as you only need healing equivalent to your max hp and not to be fully healed ).
When no monk is present delirium is good and reprisal works well enough so drk has some synergy.