Eh I think this is blizzard's fault. Even since vanilla the Forsaken have worshiped the Shadow. Thus conflating Shadow and Death themes. It's not hard for someone to see Alleria and think "Dark Ranger". I wouldn't blame them. Blizzard doesn't show the rivalry between shadow and death anywhere near as good as they show the rivalry between Holy and Fel.
There was an ENTIRE expansion debuting the rivalry between Fel and Holy... TWICE.
I hope this upcoming (most likely shadowlands) expansion corrects this problem. So that people will finally see the differences between shadow and death. But then again blizzard story telling hasn't been the greatest. They could mess this up