Taking inspirations and aesthetics from cultures and stories around the globe and sprinkling them throughout a story isn't plagiarism or ripping off.
If you can find me some story that goes "There once was a cerebrally challenged teenager that wanted to become the King of the Criminals. To do this he had to fight 7 Battlelords, 4 Monarchs, a false diety, 3 High Law Enforcers, the Supreme Law Enforcer and the super secret Master of the World plus his 5 Lord Judges" then you might have a point.
Even then though, as long as Oda has reimagined it enough to be fairly different then it still passes. Case in point, Seven Samurai getting reimagined into a western called The Magnificent Seven. Nobody is mad at that film being a genre change for a Japanese story.
Going on about stuff like Oda taking some mythological Finnish wind knot and putting that into a big arse story seems pretty silly. By this logic, are all fantasy writers that have a race of short, stout, blacksmithing humanoids obligated to pay royalties to Scandinavian countries for cultural appropriation of ancient mythologies? Lol.