i'm as big a lucas-hater as the next guy, and somewhat subscribe to your theory, but the bottom line is that Lucas was still incredibly involved in all the SW films. even as executive producer, he made contributions we'll probably never even know about that contributed to the value of the whole.
my version of the theory is that when he's worked best as a collaborator, he's done his best work. not that the SW movies are better when he's less involved with them.
and ya know what? i would NEVER take the original Star Wars away from him. sure, he collaborated on it, and got great help. but that movie was a sheer act of amazing creativity and willpower into an industry and a culture that had never seen anything like it--they'd seen the pieces he put together to make it before, but never mixed in exactly the right way.
in other words, whether the tales have been exaggerated into some kind of iconic form by time and the LFL hype machine, Star Wars was more entirely George's baby, and a much bigger risk, than any of the other SW films, and so he deserves any and all credit he gets for it. We take it for granted now, five movies later...but man. what an amazing thing to do.