Continuing the discussion on Trinity gameplay, I'd like to take a step back and survey the situation from a higher viewpoint.
So far, in my experience of MMOs, there are three stable strategies for dealing with PvE. The reason I call these "stable", is that all other schemes I've seen are "unstable". These unstable strategies always break down and devolve into one of the stable strategies.
The stable strategies are:
1. Zerg - The enemy's target cannot--or it is not worth the time to--be calculated ahead of time. Whichever player is targeted is reactively healed or protected, or forces the enemy to turn away, or just takes the hits until death.
2. Kiting - The enemy's target cannot--or it is not worth the time to--be calculated ahead of time. Whichever player is targeted proceeds to run away, out of attack range or utilizing line of sight, forcing the enemy to chase after. The chasing enemy does minimal damage, while the other players can attack the enemy. When the enemy switches targets, the new target runs away.
3. Tanking - The enemy's target can be identified ahead of time, and the situation manipulated to force the enemy to attack a specific, hardened target. While the enemy is focused on the hardened target, the other players attack the enemy freely, while the hardened target is healed and protected.
Of these three strategies, Tanking is the most interesting, the structure capable of the most variation. Zerg and Kiting are far less fun if they are the major strategy in a game.
I do not think these are the only stable strategies in existence. But I have not yet seen an MMO that has successfully executed a fourth strategy.
A "rock, paper, scissors" strategy might be stable. The classic "infantry, artillery, and cavalry" is one example. Artillery destroys the slow-moving infantry before the infantry can reach it. Calvary moves too fast for the artillery, but gets broken upon the defenses of the infantry. But "infantry, artillery, and cavalry" generally requires a great difference in movement speed, which I don't think will work in a single-character MMO .
A game that is entirely ranged might have a strategy based on cover and firing lanes. This is typical of shooter games. This strategy is rarely suitable if melee is an important part of the game.
If you want to convince me that a non-Trinity PvE MMO will work, you have to outline a fourth stable strategy. You can't simply assume it exists. Describe it, and show that it will not devolve into Zerg, Kiting, or Tanking.