Correction, in ARR people took Monk for Dragon Kick, because it had the highest personal DPS the 10% intelligence down on it was critical to survival. In Heavensward, Dark Knight had the Intelligence down and it was better at tanking most fights because most tank busters were magical which played well with Dark Mind. It's personal DPS was also not sufficiently high enough that it was viable compared to a Dragoon with Battle Litany who buffed your Bard/Machinist (or both during the final Tier) or Ninja who had trick attack and aggro shenanigans.