You guys hit it spot on. Jotaro is trying to train Josuke in this episode. He's showing Josuke the limits of his stand and showing him he can't just always rely on Jotaro and The World to save the day. There are a couple of times where Jotaro probably could have dodged or done something but he chose not to cause he wanted Josuke not to rely on him constantly. He's also showing Josuke how to counter the range limit their stands have by throwing objects. Will that come back up later? You'll see lol