@Question2 It doesn't necessarily mean the author can't see the value, he is making a story out of it, after all. It's more that the author creates this sort of unrealistic setting (or un-immersive setting, because it suspends the belief, making you question - "why don't they see the value in it?") where this pretty useful [Skill] is put down just for the sake of creating, really pushing, those underdog themes. 'Cause the underdog rising up is an entertaining story.
well you could say that the people of that world don't have google and accessible references and so can't intuit the ways that we can find it useful. The problem of his [Mapping] [Skill] is that it takes up all Slots, he has no other [Skills] to provide utility for in his team, and the mapping could become niche, possibly irrelevant or redundant, depending on a situation like going to an already mapped area to do "x" quest.
Despite it having uses on its own as well, mapping is possible even without the [Skill], albeit not with the same ease and effectiveness, the range. There are also many adventurers out there, and as one of them in the new team said "Nowadays, you can find an accurate map sold almost anywhere, after all." and there would be the [Area Map] and [World Map] [Skills] held by others, who are also willing to explore in a team, and which I'd guess holds only one skill slot , so those people have some more apparent utility than Note - [Area Map] also has the ability to "map" apparently.
and [World Map] would have all maps recorded I would guess from the description?
[Mapping] would be effective for many fields, here in our world, but the demand might not have been found yet in their setting (many adventurers, dangerous places - he has to be guarded, cause he only has mapping, already mapped places so no need for him, and other people with [Area Map] and [World Map] etc. ) The "You can just buy maps" statement was also made when they were kids (so they have some inexperience about things they haven't come to think about yet) I gotta give it that bit of consideration, at least.
there are many adventurers out there and it's a world where the concept of [Skills] exists, so their thinking and image of utility is skewed towards other things you can say
but yeah, many manga settings have that sort of trope imo, where the "useless" is actually not useless, the other characters around also not seeing the value in it, and [Skills] determining people's ranking and hierarchy (i'm not really fond of that one) and etc. the sort of forced underdog themes is really out there a lot, I do understand you - just saying things in defense of it after reading the first few chapters.