The absence of evidence is not the evidence of absence.
Lore is wrong 
. Life and Death should be placed together as part of Nature, the natural cycle. Undeath should be the seperate field, the state of neither living nor death
Granted that it’s 5 years old now, but Chronicles Volume 1 is one of the major sources we have that talk about the elements of Decay and Spirit, and the connection they have to shamans.
Their ability to transform into spirit wolves, summon spirit animals, commune with the dead, etc, are all fueled by their connection to Spirit. I could be mistaken, but I feel that you’re confusing their focus on another class (DK) with a soft retcon. They seem to forget the depth and power they’ve previously given individuals and classes for whatever lark they’ve thought up for this week/expansion/whatever.
Perhaps a, “Yes, we know this class could have done it this way, but we wanted to explore the nuances of this character this time.”