OK let's make one thing a little bit more in the forefront. Your in Camera exposure settings follow the rules, but you are looking at an extremely gloomy looking picture. There is one thing that apparently you do not seem to be considering fully and i brought it up twice before using an analogy of steak and raw files, and raw meat. Have you considered that the raw file conversion is simply under brightened? Have you considered that this could easily be a systematic importation of raw data with an incorrect profile applied? Put it this way --a raw Digital capture is basically almost black. You are trying to draw a conclusion from one Poor picture. But that picture started out as a black file and the resulting image that you can see, the JPEG version, is extremely dependent upon how the image is number 1)demosaiced and 2) how thr tone curve is applied and 3) A whole host of post processing factors such as Black point, midtone brightness, and highlight brightness.
To get back to my analogy of steak. We start with a raw steak uncooked, and the finished product is dependent to a huge degree upon the cooking temperature and time. Again, you seem to be looking for some systematic flaw in the sunny 16 rule, when in fact I would say that more likely the culprit is not the flaw in the rule but in your implementation of the complete photographic process. I guess I'm saying that I suspect The problem is more likely in the way the data has been outputted to JPEG, rather than Any inherent problem with the sunny 16 rule.
If you are not applying a good profile and this is an automated conversion from a Raw file,then the problem really does not lie in the sunny 16 rule,but rather in your image processing software,and the way the original data was processed.