Did A New Hope actually in the long run, ruin George Lucas' career?
Up to that point, George Lucas was one of the top up-and-coming directors, with THX 1138 being a critically acclaimed cult film, American Graffiti being a huge hit that was nominated for Best Picture, and Star Wars of course took over the world. However, the production of the film was absolute hell for Lucas, being constantly stressed out and almost having a heart attack.
So for the next 22 years, he took a backseat to his movies, handing the director's job to his friends while he wrote and produced. By the time he finally came back to directing for the prequels, not only had his directing ability weakened, but he had become so rich from everything Star Wars brought him that he put himself in full creative control, which is a relatively unwise idea for any director. So while Lucas made a phenomenal movie in Star Wars, he wrecked himself in the process and then took too long to get back in the game.
And don't forget that for Episodes IV-VI, he had Gary Kurtz there saying "No, that's a bad idea - don't do it." For Eps I-III, he had Rick McCallum there saying "Ok George, I'll figure out how to do it."
That and his desire to sit in an air conditioned warehouse turned green screen, and do nothing but direct people walking from one side of the screen to the other, turning around and walking back was probably a LOT less stressful, but also a lot less interesting.