I shoot RAW the vast majority of the time, but I often read about professionals who shoot jpg, and a colleague who I sometimes shoot weddings for ALWAYS uses jpg.
I'd be really interested if the debate could be 'settled' by an image that wasn't grossly under or overexposed in the first place but was rendered significantly poorer due to being shot in jpg. I guess the ideal would be an image that was shot in jpg + RAW and the two shots optimally processed and the outputs showing a significant advantage in favour of RAW.
I am afraid even that will not give a definitive answer as it still relies on the intentions and skill levels of the photographer and even the suitability of the raw processor used.
You can find very similar arguments about which is the best raw processor for a particular camera.
the output of a raw file starts from the same captured data from the sensor. in the case of a jpeg the camera manufacturer has made all the decisions on how it should be processed... creates the Jpeg and discards the rest of the data.
A jpeg made from the raw file at a later date by the User, allows him to impose his ow
n preferences on how the resulting image should be displayed.
He can then.... create his jpeg. but keep all the camera data in the form of the original raw file.
Every time a Jpeg is re saved or reprocessed, it is compressed and artifacts added. The image is degraded.
This is not so with a raw file, as it is only used to create a new first generation Jpeg or Tiff, it is never altered itself.
From any raw file we can produce an infinite number of different new first generation files all as good as the first.
All your solution would test, is the relative abilities of the manufacturer to create that first Jpeg in a way that suits the subject, and to your taste.
And your own skills to process a raw file and to produce a jpeg from it, that better suits the subject and your own preferences.
However using a raw file also gives you the option of producing a uncompressed tiff file with a higher bit rate, for those occasions when you want to manipulate the image further in a program like photoshop, or for the production of extremely large images.
Better can mean many things ... including better for what.