Let’s think through the problem. I think the purpose of (the rather awkward) UniWB is to make the JPEG driven histogram in the camera behave as if it were a raw one. This ruins the JPEG and so there is no point using the JPEG+RAW mode as you have.
To approach this problem, I would first need to take a photograph of a evenly soft illuminated grey card near saturation. If I know the properties of the card and lighting, I would know what WB, etc., settings to change to make the histogram behave in the way I want it to.
Now here are the multipliers that (I believe) you should be examining. I say “(I believe)” because I haven’t done this in a long time and every camera has different metadata. If I recall correctly, you could ask exiftool or maybe it was exiv2 to expose the full name of the tags to make sure you have the right one(s).
Measured RGGB : 403 1024 1024 637
Measured RGGB Data : 6184 15598 14938 9164
If these are the correct ones, then you can clearly see that the ratio is off from R=G=B. Clearly something is wrong. If I recall correctly, Mr Kasson’s quick method depends on your monitor being calibrated / profiled in a particular way.
I noticed something else in your metadata.
Picture Style : User Def. 1
Picture Style User Def : Standard; Standard; Standard
In my opinion, it shouldn’t be Standard but Neutral. If you don’t have Neutral, then Faithful. Basically, turn down or off anything that would affect the JPEG and make it more abstract from what the “raw” output would be (e.g., sharpening, non-linear modes).
PS I noticed that your dcraw output says
3692 as saturation. At 12 bit, it should be
4096 as the max value. I wonder why dcraw would use the former value…