I'm also wondering if sigma is doing something weird with sharpening.
They do seem to readout the full 6K of the sensor,
because of the 21ms of rolling shutter, but then the DSP seems to
Downsample the 6K into a 4K Bayer pattern.
(Unless you enable Super 35 Mode, where it does a 1:1 Readout)
The result seems to be different from Sony or Pannasonic, who use similar tech.
But the image ends up losing details,
having more problems with False color artifacts and more Moire.(On the Sigma)
Slashcam mentioned it in there review, which I think is only in german.
Where they noticed artifacts, which didn't show up in the comparison with the
I'm not sure if I can link the article.
Maybe it is a Hardware issue with the DSP, or maybe it isn't and it can be fixed
with a firmware update and they just didn't fine tune it yet.
Maybe they are already working on it, because of what you said, in the
Slashcam Review, the MOV mode had even worse Artifacts(which might be because
of the older firmware.)