your contradicting yourself, you both say he should be bait (he is) but also they shouldnt have dangled that bait and focused on defense
if the ghost doesnt want to be found it wont be, thats not limited to D ghost, they have to make the ghost think they're vulnerable or it just leaves them...
i think the core concept of the ending is just terrible, just gives up the book and the demons just leave and thats it, everything he spent the series working to obtain ended up being a complete waste of time
there needed to be some third option where he could find a way forward that everyone...