Not to take anything away from Ridley's visual brilliance- he has after all made a couple of the most visually iconic films in history, but Cameron is more of an all-round mastermind. He was a screenwriter first, where Scott came more from the advertising realm. Cameron directs actors in a way that Scott doesn't. If you listen to a lot of commentary on his films, it's pretty evident that he's more hands-off when it comes to actors and it shows.
I do listen to commentaries and I am aware of both of their backgrounds, and I agree with your assessment.