Are questions about these series on-topic?
Tough, I also had thoughts about it. I believe that by definition, we should not allow such cartoons, because we need to draw the line.
The line should be drawn at "Anime & Manga only", which by definition is only Japanese.
I recently watched a Youtube video where an American asked some Japanese people what their favorite manga and anime were. One girl answered that SpongeBob was her favorite "anime".
It seems to me that Japanese people don't make the distinction between western cartoons and anime like we do. Therefore I'd rather be on the permissive side when it comes to which content is allowed or not.
On the other hand, I do strongly feel that there must be at least some Japanese influence to the show. Otherwise this site might just as well be called the Cartoons and Comics SE.
I agree that Korra/ATLA and Samurai Jack and anime-inspired Western shows should be disallowed.
However, I do feel that manhwa should be on topic. A lot of manhwa / manhua looks just like doujinshi or independent manga.
To clarify: I don't think anything that "looks like" manga should be on topic here. However, manhua and manhwa are the products of Japan's historical dominance of East Asia, both economically/politically and culturally.