Not my point. He doesn't need to write One Piece to make millions a year. He could legit quit right this second, and at most he loses his annual salary, which is peanuts compared to the tens of millions a year that he's going to be making for the rest of his life off of royalties. He doesn't have to milk anything. He's set for life.
Royalties is where the money is made, not his piddily little salary Shueisha pays him for writing One Piece.