Firstly there's a very huge difference between copying and using as inspiration. Secondly Oda has used a ridiculous amount of different movies, books, series, stories, legends etc. as inspiration for hell of a lot of things. So that he would use American comics is really nothing unusual, he has even used Belgian comics.
The examples you use however are extremely poor. The Amazons are a fictional female-only society from Greek mythology where they even cut off one of their breasts so that they could shoot better with a bow. The Amazon river was also named after them as when European colonizers arrived in South-America, they immediately had to think of that mythological race of women when they saw the local population. This is also where the American comics got their mustard from for Wonder Woman as she's an amazone. It's higly doubtful that Oda, who knows about Greek mythology, would base Amazon Lily on Wonder Woman rather than the original source.
Joker and his appearance are meh. Even if that would be the case, nothing special here as he also has used Cervantes Don Quichote as inspiration and so many other things.
