WHile GM/Ford had their share of truly hideous and embarassing designs, it really didn't matter. They could have been handed the Camry design and still bollixed it up.
Case in point: The Ford Contour. It was originally sold in Europe as the Ford Mondeo. It did very well there, was well regarded, and was a very reliable and well built car. Ford brought the design over to the US, and had UAW workers build it. It turned out to be a total disaster - one of the worst cars Ford has ever sold in the US because the QC and build quality was so bad.
You're probably right that GM would have wrecked the Camry due to an atrocious workforce.
IMHO the Big Three got the unions they deserved.