From most the other chapters, I feel there's an excuse, but this is just not believable. It changed from a tragic adventurer party's story to a shonen, just like that. Imo, if the arc was given more time to develop before concluding things, it would have faired much better at least. (I know this isn't the end of the novel, poor choice of words, mostly on the title of the chapter's part.)
Edit; I use tragic loosely, this seems like a first timer's go at this. Never publish your first tries unless they're speedruns.