I was thinking, what the parshendi's goal is to to die but not because they are forced to serve odium? What if it is like the old norse myths were dying in different ways meant you went to a different heaven? Perhaps the Parshendi are like the vikings in their reason for needing the gem hearts too, the vikings only pillaged because they lived so far north and couldn't support themselves on what their land produced.
This still doesn't explain why they broke the treated hours after they signed it, but hey its a thought!