I had a thought, and I realize that I am late to the party with this thought, but I wanted to share it anyway.
John told Merle to sever the bonds, right? That was his hint for defeating the Hunger - sever the bonds. And at the time I thought that was strange advice. Bonds had been portrayed as a positive thing up to that point; why would something as negative as the Hunger have something as positive as bonds?
The reason is, bonds are not inherently good. A person can be bonded to a bad person, a bad thought, a bad perspective. And like the Hunger consuming worlds, that connection to negativity can consume a person.
Something like the Hunger is only as powerful as its bonds, as the number of people it hurts or, in the beginning, the number of people who bought into its perspective. In that first world, everyone decided to follow that path - what would have happened if one single person had said “no, this isn’t right”? The shield that Lucretia made was so effective because the Hunger is nothing if it cannot feed on people. The Hunger is nothing without bonds.
If you can, sever your negative bonds. When something isn’t right, say so. When you’ve become too tired to fight, ask for help. Surround yourself with light. Don’t feed the Hunger.