@megaeraerin
It has always been this way, there's been no pretense about it. Regrowing heads and resurrecting cats have been around since the first few volumes. The precedent that destroying someone's devil tumor is what qualifies as actual for real death is established pretty early on if you pay attention. Bodily destruction is an inconvenience and an avenue for plot complications, not character removal. It's not plot armor, it's an established aspect of the setting.