Once again everyone is hyped up for another game which promises to do away with the Trinity of tank-healer-dps. This time the game is EQ Next. I am deeply skeptical of this claim. I'm not saying that the Trinity is necessarily the best system for PvE. But so far, no one has demonstrated a better system.
I've seen various people saying that EQ Next will feature complex AI, which will obsolete the idea of the Trinity. In my view, if the system does not work at the simple level, making it more complex is not going to improve things.
Let's take the very simplest PvE scenario. We have a knight with sword and shield and a barbarian wielding a two-handed greatsword. Both characters are fighting an ogre in melee combat.
Who does the ogre attack?
This is the simplest decision the AI has to make. The knight's shield improves her defense. The barbarian's greatsword improves her offense.
Logically, the optimum path is for the Ogre to attack the barbarian. Generally, the rule of thumb is that you first want to kill the highest offense or the weakest defense. The barbarian meets both those criteria. And indeed, this is what will happen in PvP.
But the archetypes of fantasy demand that the Ogre attack the knight, to take the sub-optimal path. That is the very point of the shield, to take the blows. The shield is a pointless choice if no one is attacking you.
So no matter what, to stay true to the soul of the fantasy archetypes, the ogre has to attack the knight. Trinity systems do it very simply by introducing the concept of threat, which is linked to--but not equal to--damage. You could also do it by having the knight "intercept" attacks made against other characters. Or perhaps by turning the knight into a source of debuffs strong enough that getting rid of the knight first becomes optimum.
Another path might be making the knight do the highest damage, making the choice harder. This probably won't go over too well with the barbarian, though. And it doesn't match the archetypes.
It is trivially easy to make a more competent AI than the Trinity system. The harder task is making one that leads to fun gameplay and yet stays true to the fantasy genre.