When I get home from work I'll play with it a bit.  But I don't think the clouds add anything, compared to the blue of the sky and the yellow of the balloon, which is one of the naturally great color combos, the clouds are a very weak element, clone e'm out.  For an image like this I don't thing that a gradient is the best solution, it looks good against a horizon because of the nature of the lum. of the sky, but there is naturally very little gradient when looking up.  The balloon with a slight bit more saturation against a plain, well saturated sky (shifted toward the blue spectrum from cyan) is about as strong as this image can get, IMHO.

SS have the most random, non-sensical rejection reasons in my experience (working with 14 agencies). There is nothing to learn or improve from their rejection reasons like the 'lighting' reason above, and that's what I see as the main reason for photographers to be receiving the exact rejection reason.