But GL didn’t hardly have to do with Empire at all other than the idea and the early draft. His draft was revised, then that revision was rewritten several times by several people. Lucas was like, standing to the side of the helm, looking at something else.
I will reply to this as the “source” you provided did not support any of this.
Regarding screenplay, after Lucas wrote the story outline he hired Brackett to write a screenplay based on it. She finished the her draft of screenplay days before she died (she was terminally ill while writing it). Lucas was unsatisfied with the screenplay and basically had to discard it. He then wrote his own draft from scratch (while also making some storyline changes). He then hired Kasdan (who he impressed him with Raiders’ screenplay) to improve upon it. When it comes to scenes Lucas draft is pretty much what ended up in the film. However, Kasdan significantly improved the dialogue (they had several meeting to discuss things). Lucas withheld his draft from the WGA in order to ensure Brackett would get a screenplay credit, otherwise most likely Lucas and Kasdan would get the screenplay credit.
Regarding conceptual art and visual design, Lucas directly worked with McQuarrie and Johnston, who visualised his ideas.
As for principal photography, it is only reasonable that Lucas came to the set only few times. He hired Kershner to direct the principal photography so he could do other things in the meantime. If he wanted to be on the set on daily basis he could direct actors himself.
Regarding budget increase, Kershner was working slowly (many takes, forced actor to improvise scene instead of giving exact directions). The film went over-budget and over-schedule. Principal photography on ESB lasted six months compared to three months on ANH and ROTJ. So I would say this alone can be the reason for better acting in ESB as huge amount of time was spent on it.
As for editing, Lucas pretty much worked on the final cut with Hirsch (Editor) in the post-production in a normal fashion.
So I would say Lucas was creative director behind the film.
Just out of curiosity, where does this come from. I’m not saying I don’t believe you, but a link to something or a “from [insert source]” would be nice.