Of course I agree with this -- Lucas could never have done it alone. And his ideas were made better by others, specifically McQuarrie. And he never could have known what Williams would contribute in that score.
And I'm no Lucas-lover, believe me. But you got to give the man his dues. His idea, his world, his Jawas, laser bolts instead of beams, hyperspace, the Falcon, the idea of mashing history and fairy tales to make a modern one, the Vader concept, the 'used' universe, on and on -- Lucas had a vision that in its time was simply amazing. Many borrowed perhaps, but no one put them together like he did.
I think to say Lucas was just lost and somehow got lucky is naïve and spiteful... and quite honestly, I'm shocked that this is coming from you of all people. Lucas was quite innovative in his thirties (American Graffiti, Star Wars, Raiders, THX, etc). I believe merchandising -- and the money he once hated -- corrupted him and 'destroyed the good man' that once was.