>>5141134You unironically will become good. Whether you will be as good as Oda, better, or worse, depends on many factors, such as your starting skill level, your ability to analyze your own art and learn from your mistakes, and your curiosity and desire to go outside of your comfort zone and challenge yourself. Obviously, the type of manga you do will influence your progress. If it's a shoujo romance where you can get by with just knowing how to draw a face at 3/4 view, you will probably not get as good as Oda. If it's an action adventure story, like One Piece, you're going to improve a lot regardless.
