Here we have an expansion that claims to be devoted to class fantasy and identity, and making each spec feel unique. So why would they bother with adding a new class? Wasn't the whole point of these class redesigns to keep the classes fresh and unique? Why would they decide to waste development resources on creating a new class from scratch given the downsides?
1. The developers working on the classes are now stretched over a larger number of classes. Which means less development time for every other class. Less time to iterate and respond to feedback, etc. There was simply no time left to respond to any of the other class concerns in the Alpha and Beta, and much of that can be attributed to the addition of DH's and taking those resources away.
2. The significant initial time investment required to create a class from scratch has also taken many resources away from many other classes that clearly needed more attention (e.g. Hunters).
3. It is counter intuitive to their goal of class fantasy and identity. Adding more and more classes dilutes the identity of the existing classes, particularly when iconic spells from other classes are taken in order to create a functioning class. We've now got 4 mobile Leather AGI classes and each one feels mediocre because it's been done so many times. We also already have 34 specs in the game. Did we really need more?
I think that the decision to add a new class was the wrong decision. It has clearly negatively impacted the development of many of the existing classes, and I would have preferred them to polish the existing 11 classes before diluting the class base with an additional class.