The Dunning-Kruger effect is just not about people who are bad at something and don't understand that they're bad, it's about how hard it is to assess your own abilities.
> Moreover, competent students tended to underestimate their own competence, because they erroneously presumed that tasks easy for them to perform were also easy for other people to perform.
https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect
Usually when someone is really good at something but does not understand that they're really good at it, it's fine. You get it, the guy's an expert, you'll give him some leeway. Sure it can be annoying to talk to that person, if their subject of expertise comes up, but generally it's fine.
The MC in this story is good at everything that the story revolves around (adventuring), and is totally clueless about it. That's what makes it weird.
The story is basically about a guy with severe lack of self-assessment... I'm not sure that makes an interesting background.