Yes, world building. That works. As the concept of making the author creating the backstory of why every evil villian became an evil villian would be within the same argument as yours.
Instead of "hand waving" evil villians just to come into existwnce, we must delve into the reason why the evil villian became so.
We would run into an argument whether or not it is necessary to make backstories to explain every evil thing origin story to make the story too long, or it turns it into a filler. Or we could argue if the backstory is too short if the author explains the reason in a single page and makes a "weak" "world building" experience, as per you say.
World building isn't a problem, but the author can run into issues of getting side tracked too much, and he just started the story. A lot of people have short attention span due to things like twitter and youtube shorts. Its not like we are hundreds of chapters in. You need to keep the audience entertained to put food on the table.
If you want a well fleshed out manga at the start, either the author must be a seasoned pro so he can ignore the publisher warning about getting side tracked with "world building", self publish. Or you can read books. Like fiction books.
