Personally, I didn't really find his 70s concept for the prequels all that interesting. I mean, he could barely tell about how Vader came about in three movies, I can't see him doing it in just one. And I think that focusing each on just one topic would be pretty boring.

One thing that you simply nailed (as well as many other people) was his lack of another writer, as well as following their suggestions. If only the other prequels could have been like Episode III - despite its own flaws.