Japanese mangas are placed more importance stories and charas than drawings.
The editors must control their quality.
Great successful mangakas also are discussing ideas with their editors.
Moreover, a mangaka can be supported by plural editors, an editor can take counsel another one.
Diversity gives quality to a manga.
Generally, a mangaka works individually until inking over a pencil and finishes it with assistants.
The coordination of work sharing depends on mangaka.
Some mangaka draws only neemu and leaves all of the process with assistans.
But no mangaka draws manga without an editor.
In Japanese publication culture, manga is a commercial product in a sence.
It may limit a mangaka’s imagination in drawing, but guarantees the quality.