The 'possessed' ability says this:
"if this triggers, this takes place instead of any other death effect."
But it isn't stronger than the other death effects like the Berserker, Knight, Possessed(the ghost), Feather serpent, Supplicant. Maybe only the text of the possessed is wrong not how it works.
Interesting interpretation, I agree with you that interrupting berserkers, FS, supplicants, and skin walkers would be cool. But I disagree with the knight.