Models with higher polycount is a solved problem for them, otherwise they would not be able to implement pandas in its current form.
(Normalmaps would not really help with models that are so low-poly, also you just transfer the performancecost to something else, which is not cheaper at all.)
See the small increase in extra smoothness in curves by adding extra polygons and the increased density in polygons used in the face.
it's clear the extra polygons are being invested in areas that will be visible, it's not like pandaren have a high poly bellybutton
These extra polygons in the face are what allow the model to have so many facial expessions, that's something that just isn't possible with the human model.
The problem is that a character designer works with a poly counter which is sat to a upper limit. Afaik a naked Wow model is around 5-6 k polygons. But when you add armor and weapons, you will at least double that count - and then you actual start approaching what is feasible for modern mmo games. If you add polygons to the naked model, you might have to cut down on the armor/weapon details.
You can get along way with Normal maps, which sort of "paint" extra polygons on a model. But im not sure wow`s graphic engine supports that kind of texture.
You have literally no idea what you are talking about. None of that makes any sense at all. Care to explain how the Pandaren model exists?