Lucas seems like the well-spring of ideas here. He goes on long rambles, almost free-associating, and then Kasdan or Spielberg will have a one sentence reply. And then another rant. It's like they're providing minor course corrections while he generates ideas and ideas and ideas...
Anyone familiar with writing rooms or the like, is this asymmetrical pattern common?
I've participated in storyboard brainstorm sessions (more on the design/drawing side) and the kind of asymmetrical energy you're talking about definitely exists. Largely depends on the personalities in the room - if there's one particularly "extrovert" personality that tends to think out loud, the others tend to shift into an editor mindset.
It sounds like Lucas has been thinking about this for a long time and has already worked on it a little with others + done a little research, whereas the idea is newer to the others.
Lucas had been thinking about it for a while. His initial premise was some kind of Archeologist James Bond type action/adventure film that pays homage to the Saturday matinee cliffhanger serials Lucas enjoyed as a youngster.
Anyone familiar with writing rooms or the like, is this asymmetrical pattern common?