What's going to be the strength of Dark Knights now?

[MagiusNecros]

And then you create a situation where classes are kicked to the curb for not meeting whatever arbitrary requirements are set by the encounter design or players themselves.

It'd be one thing if we were talking strictly gameplay with the same results between classes. That actually works at keeping everyone viable while providing different play styles. As an extreme example, if I hit Shield Oath to mitigate 20% damage as a PLD, a new job might need to stack temporary buffs from combo abilities in order to meet that level of mitigation. So a super l337 haxx0r guy can play the new class and a lolcasul like me can play PLD, and both of us are viable choices for a tank.

Differing playstyles such as...?

[Duelle]

Differing playstyles such as...?

I'll outline some general tank gameplay, so I don't have enough time to do a full write up of several classes.

Tank 1: Passive mitigation via a defensive stance. General-use cooldowns that mitigate damage.
Tank 2: Active mitigation tank. Has to manage resource recovery and generation in order to mitigate hits on set intervals, with abilities that can be used to survive tank-busters. Mathematically is the same as tank 1, but has to press more buttons and keep an eye on resources to be competitive.
Tank 3: Upkeep tank. Relies on secondary effects from attacks in order to achieve mitigation (certain attacks grant Defense Up, Evasion Up, Parry Up and so on). Mathematically the same as tank 1, but is much more reliant on their physical attacks to also allow them to reach the intended levels of mitigation.

Tank 1 is perfect for someone like me, who likes simple and straightforward gameplay. Tank 2 is more for the risk/reward type of player. Tank 3 is for the player that likes to constantly press abilities.