Actually Kershner designed the storyboards for ESB himself, and was active in script meetings, and in meetings with the art department. He wasn't just shooting shots that Lucas designed, he was shooting shots he had planned, with some improvisation to boot. The scripts for ESB and ROTJ were not purely Kasdan writing down Lucas's ideas. Lucas, Kasdan, and the respective directors all brought their ideas to the table. It was Kasdan, for example, who said that Leia and Lando should both arrive at Jabba's Palace in disguise, and that Leia should strangle Jabba. Lucas's only contribution there was modeling the scene after The Godfather. For story meetings, everyone was an equal player.