As I said in my post above, I think Kurtz gets way too much credit sometimes. As for McCallum, on whether he is a good producer, from a financial point of view in the PT, he is a big success. But SW goes further than that if you look at each movie.
The original SW was almost a disaster, and if I were on the set in 1976, I probably would have thought this movie was a bomb waiting to happen. I give Lucas major credit for the success of the original, and I think he deserves everything he earned for the original, cause that was his vision, his directing, his writing.
ESB was definitely more collaborative and that is its greatest strength. I feel if Lucas wrote and directed ESB it would have not been as good as Kershners ESB. Now that isn't a slight at Lucas, but Kershner put a different touch on the movie, it feels like a totally different movie than the other 5 SW movies. Now I still love the original more than ESB, but ESB is still a classic, and I also feel the other 4 SW films have not even come close to the first two in quality.
What I am getting at is ESB is the only movie where Lucas kind of let someone else take his SW vision and make it their way. Mostly cause Lucas was starting this huge business, and really didn't know if people were going to turn out like the original SW. But to everyones suprise, alot of people liked it more than the original, except the kiddies like myself. At 8 years old, I did not love ESB like the original, but in 1983, I loved ROTJ! 20 years later, I still love the original and now love ESB, and think ROTJ is good enough to end the trilogy.
After ESB was a success, Lucas knew he had a fanbase that was loyal, and that is when he stopped taking chances. I give the Jerry Maguire analogy whenever I go to a SW movie whether it is a good movie or a piece of crap like TPM, "George, you had me at the opening crawl!"
After ESB & Raiders of the Lost Ark, I think Lucas, who probably had this grand vision of this huge movie saga of SW, didn't feel like doing it for the rest of his life. ROTJ was a basic sequel, no chances, recycled death star, the heroes all win in the end, and everyone lives happily after.
I believe Kurtz when he says Lucas condensed everything from 7,8,9 to ROTJ, but that also tells me all they had were rough notes. To me I think they ran out of story with ROTJ, cause the only new interesting plot point was the Vader/Emperor/Luke conflict in the last 30 minutes, everything else in the movie is either recycled or going through the motions to end the series.
Should Kurtz get all the credit for ANH & ESB, or even more than Lucas? No, I don't think so, cause every movie is Lucas's vision, and his story in the end. But what makes ESB one of the few sequels in the history of movies that is as good or better than the original, is there were other people leading the charge on it, while Lucas was in the backround, and that is why it feels different.
Personally, I don't think Lucas liked the way ESB turned out, it didn't have that B-movie 30's style feel to it, in which ROTJ, TPM, AOTC, and ROTS definitely do. The original SW had that, but it was able to conjure up movie magic and such a basic story and great characters & pure emotion at the end, that it is a classic despite it trying to be a B-level movie.
The PT has made me realize that ESB was the pinnacle, and sadly, I don't think we were going to see any great movies after that. SW fans like myself, since 1980, have been waiting for the next ESB type movie in the SW series, and unfortunately, it just wasn't going to happen. Lucas hit lightning in a bottle twice with SW & ESB, we should be grateful for that, but after that we had 4 mediocre movies that sold because of the name SW. I don't think we can blame anyone including Kurtz, I just think Lucas never really wanted to make these movies as great as we expected.