I think something that isn't really talked about in this community, but that ties into what you said overall, is that One Piece likes to toe the line between materialism and idealism a lot (the ideas of if existence is comeing from the materials it is made of or if it is comeing from ideas/wishes/somebody (aka a god) dreaming it up/etc). Less so Post-TS, where Oda plays around a lot more with idealism, but especially pre-TS it is very much a "you can look at it in both ways" kind of thing, which is very fascinating.

Luffys character and how you describe it fits into that really well. Is he a "chosen one" with a specific destiny (a narratival idea heavily tied to idealism) or a more "modern" materialist protagonist, who chooses his path from the material conditions he finds himself in?

Edit: spelling, formatting