I think Lucas kept Brackett's name for screen credit as a tribute to her and to bring more attention to her work.
The original ESB script is very, very different from the finished product. Vader is not Luke's father, the ghost of Luke's father appears, Han doesn't get frozen in carbonite, a subplot involves Han trying to find his step-father, who controls all non-military shipping in the galaxy to join the Rebellion, etc.
The original ESB script is very, very different from the finished product. Vader is not Luke's father, the ghost of Luke's father appears, Han doesn't get frozen in carbonite, a subplot involves Han trying to find his step-father, who controls all non-military shipping in the galaxy to join the Rebellion, etc.