If you look at the measurements for 32 ohms, every graph for the sansa clip are worse than the cowon J3, except the flat frequency response. I guess , the gap is even worse when using my 42 ohm headphones.
My conclusion from these graph is the sansa clip have great sq, with a 16 ohm or lower impedance headphone only.
A flat frequency response isn't enough to ensure a better sq.
A flat FR does ensure accuracy and that to me is better, what is "better" is entirely up to you. You may fancy all those sound effect features from Cowon players; I personally left everything off and as unprocessed as possible when I had them.
I think you should do some googling for "sansa clip+ measured" if you really want to know if your conclusion is even close to the truth.
Hardware analyzers are far better than RMAA if you truly want an accurate picture. The only reason why we always see RMAA results is because most people refuse to spend over $10,000 for such analyzer if not using it as a purpose for design.