I somewhat disagree, Kisai. Both the tank and the healer AI need some work. For instance:

-Tank: The major offender is the mob backtracking. Let's say you click on "engage". The DPS (if you have ranged) will start attacking them, however the tank will move where the mob WAS, while said thing is already attacking the DPS. In places like Wanderer's, the tank would go back to attack the adventurers fightning the Wandering Tonberry.

-Healer: It seems like they don't enjoy healing themselves upon taking damage. The healing is scrambled, as it uses medica II even when the fight is over. On big pulls, they would let you die but granted... big pulls is not "playing as intended", and the healer potentially has a "gambit" that would heal you upon reaching certain threshold of your HP.

Their resistance depends on their selected tactics. If you go full offensive, both the DPS and healer will be a bit squishy. Specially when they step in the bad.

I'd believe that the DPS are working as intended because well... they just attack things. They don't interact as much as a healer or tank, as they have a different playstyle.