If his issue is that he is so good that he makes authors useless then why doesn't he turn into an author himself? Or an artist, if he lacks the imagination to write his own stories. I'm pretty sure that there are a lot of manga written by one guy and drawn by a different guy.
Why do editors even care if their authors becomes useless? The chapters are still coming out in time and in proper form, right? Who cares if the assistant is doing 99% of the work?
And why I'm asking so many questions in the comment section of a manga about a young girl who can only draw if she masturbates?