while Lucas was creative director behind the film.
Well, he wasn’t very involved with the film during production, so I wouldn’t really say creative director.
Well if by production you mean principal photography then you are right. After all that is when actors are directed and scenes are recorded, which was what Kershner was hired for. However, when it comes to creatively most important elements such as story, main ideas, screenplay, working with visual artists (McQuarrie and Johnston), etc., it was pretty much Lucas at the helm.