TTK sounds like something to be aware of in balancing pvp, but I’m skeptical about the ability of a simple metric to balance a pvp game which is actually interesting and enjoyable to play.
The first point is that GW2 is about capping and holding points, not just killing the enemy. So already TTK is limited (though still relevant) in how it can help us balance GW2 pvp.
On a basic level TTK seems better suited to a 1v1 game than a team game, where you want interesting abiltities to interact with each other. I also think that the difficulty of execution is an important factor – if one class is much easier to play perfectly, and the other is nearly impossible, then I would not say they are balanced although they may have the same TTK under your assumptions.
TTK also does not seem to take into account the value of support abilities like healing and control. Now maybe you want to build a more complex model that can do this on a per-group basis. Maybe with healing you can do it since it is pretty linear, but what about abilities where their timing is important, eg control abilities like stun and immobalise, how do you assign them a rating? These are abilities that might have no TTK impact if you do them at the wrong time, but very high TTK impact if you do them at the right time. To factor these in requires some subjective judgement I think, which means were are not just relying on maths anymore.
In this regard I don’t think you can model a fluid and dynamically interactive game like gw2 on a computer, where timing is so important to the result and there are so many possible permutations. Due to the interactivity of the various elements, the analogy here would be with quantum states rather than classical physical states. It does not take many qubits to make a quantum state unsolvable for the most powerful computers.
You can see these issues more clearly in a game like lol, which has more defined roles and abilities. A lot of champions are valued because their abilities enable a particular strategy or are useful in a particular context. For examples, a team might want a champ with a good initiation, or a good peel, or maybe a global map presence. How can you balance those around TTK? I’d say you can’t because they don’t have anything to do with TTK. They are about allowing a team to implement a particular strategy or get an advantage in particular circumstances which the team will then try to produce during the game (eg this team comp is bad in team fights but good at split pushing, so we need to avoid team fights and split push to take their towers). I think that if you wanted to expand the TTK concept to address those abilities you are diluting it to the point were if ceases to be a mathmatical model and instead becomes a format for ordinary stragetic judgment.
Now you might way, well GW2 does not have these kind of defined roles, so TTK is more applicable here. That is a fair comment, but it brings me to my final criticism. Is TTK the best way to design a team game which is interesting and enjoyable to play? I think GW2 PVP would be be better if it had more of the kind of strategic depth and variety that did not lend itself to TTK modelling.