The way Lucas described “book three” back in Dec 1975 says otherwise:
“In the third book I want the story to be just about the soap opera of the Skywalker family, which ends with the destruction of the Empire.”
The Making of Star Wars (JW Rinzler, 2007). It was during a story meeting with Kurtz and writer Alan Dean Foster. In it, he also said that at the end of the second book, “we find out WHO Darth Vader is”. (emphasis mine)
Those Making Of stories have long been shown to be Lucas revision many times over. No different than his attempts to revise history in other written forms, documentaries, and interviews.
Sadly, I don’t believe a single word he says any more. He’s lied so many times over the past few decades that whenever I hear his voice or see a written piece, I automatically assume he’s lying. It’s what he does. Whenever he gives an interview, he might as well be burping the alphabet.
On the Star Wars website, they don’t exactly shy away from the fact that he tries to change history. Here’s a link about the invention of Midichlorians and how they didn’t exist in 1977, regardless of what was written in Rinzler’s book.
“Please note: While we were preparing the text for The Making of Star Wars, Lucas added a note to this passage about midi-chlorians, bringing his original words in line with his later thoughts…”
Lucas wouldn’t have been discussing a second sequel two years before the original film even had a finished script. It didn’t even have a finished story at that point.