So over telling the story that portrayed a "barbaric horde who ravished noble human lands" falls inferior to vague portrayals / implication and what they create in our imagination?
I think its overdone in the wow universe so much at first that the obvious of certain central themes is very easily lulled over. The story of the sha and how they manifest from within, how the old gods represent very archaically symbolically persistent themes in human culture.
How much surprise do you expect there to be when you dig deep at what the God of death shall be. Sure you could tell it 50 different ways, but they would all sound obvious for the God of death, common sense would anticipate where the story goes.
The weaving together of different themes is what I think warcraft is becoming more. They've built a fairly strong basis to expand on things like light vs. Nature death vs. Void etc. But I think they needed to get everyone on the same page with the story of "this is what death is" before we could really understand the future in the story as it is told. After all it is a story, they've just drawna line i shadowlands and defined death in their universe, maybe we redefine it in 10.0 but I think its the start of more complexity with the pieces you listed that they've only recently defined more wholly.