So basically to justify taking DRK on a raid you have to not have a MNK in the group, be fighting a boss that deals primarily magical damage, is preferably but not necessarily parryable for access to reprise, and have the ot be a warrior willing to use deliverance because lmao sword oath paladins.

However, both Paladin and Warrior can maintank these fights equally well, without the arbitrary requirement that the boss have a significant magical attack, and be fully optimal to slot in any standard 2-2-4 party composition.

So, we've laid out the long list of arbitrary requirements needed to justify a Dark Knight in the group. What advantages does this afford the group, if any, that could not be had by replacing the Dark Knight with a Warrior or Paladin and allowing for more flexibility?