Just seeing the sample images (and I'm not giving conclusion) I admit.
All the sample I've seen from the 5D3 looks way too soft. It can be 2 things : First is post prod NR. Second is 5D3 NR. If It's the 5D3 NR they use it wayyyy too much.
Ok nice, you see no noise at 1600 ISO or even 6400 but it ruin the quality.
Aside from the possible bad judgment and/or low talent of the people Canon chose to shoot their samples, I've come to almost the same conclusion as you have, but I'm just not quite as sure as you are, and I would like to see images from raw, shot by a good photographer and processed in DPP by a good craftsman before I could be. If, under those conditions, the results from raws look great, then I'd have to say that Canon has rolled up a big fat fail with its 5DIII in-camera Jpg processing.
But, there is another possiblity that is something I have deduced from the available specs and samples, plus statements by those associated by Canon with the 5DIII release. It's possible that Canon, in order to satisfy the potential video users of this camera who had previously complained about the bad aliasing and moire on 5DIII video, has used a much stronger AA filter on this camera to help cure it, and that the softness you see in the released Jpegs is mostly from this. There are two other points that can support this. One is that Canon is offering the unprecedented function of supposedly deconstructing the effect of the AA filter in the latest version of its raw software converter, DPP, to be released with the camera. Why do this now, unless it is especially relevant to the 5DIII? Although this might be their software answer to the Nikon D800 without AA filter, I doubt Canon could have developed this software function in the short time after which they likely learned of Nikon's plans. Also, in looking at many of the Canon 5DII samples, I noted an unusually low level of moire in many of the samples, several of which I know would certainly have displayed some level of moire if shot with my 1DsIII. I hope I am wrong about this, but I am afraid that I may well be correct in my deduction.
Second, as I look to the image, it look photoshoped! In some of them I can see clearly bad photoshop!
I think that we really have to wait unofficial pictures.
Most likely what you are seeing, and I too, at first, suspected as possibly some sort of horrible Photoshop work, is rather the awful effects of using the new in-camera HDR function, which, at different settings results in effects that range from bad to absolutely pathetic. This function needs either to be vastly improved or deleted from the firmware ASAP.