OK, so I tried Minilux and it does allow for shooting full resolution in 16x9 mode. yay1974's XML bot burial work well with it, although the app will crash if you change lenses to telephoto. Also, the viewfinder on the phone's screen shows 4x3 frame even when Post-processing set to crop, so framing the shot is not precise.
So, I am back to burial's latest version, with yay1974's latest XML (2.2). The 16x9 shots are 9MP instead of the 20.4MP from the stock camera, which is a problem for me, since probably within my life time there will be large TV screens which will max out the 20.4MP resolution (although maybe AI will be good enough to upscale flawlessly).
Anyway, thanks to yay1974's suggestions, I turned off Tone Curve entirely (even boosting black to +30 was too dark).
And WOW! It's just about perfect! The color balance is up there with the iPhone and IMO, better than the Pixel. Seriously impressive!
Thanks again, yay1974!
Now, if we could only get full resolution 16x9 with proper viewfinder ratio, this would be perfect.
This was for the main camera. Now a question on the 3.7 telephoto:
With yay1974's XML, there is a strong blue tint. Is this by intention, or is it something on my end? Also, the stock camera produces slightly larger pixel count (6MP) and smaller file size (3.5mb) than GCam, which is 5.1MP and 5mb. In addition, the stock camera shot is closer, more zoomed in, while GCam is less zoomed in -- what's the deal here? Is it because Xiaomi zooms in in post-processing? It would make sense, because the stock camera has a lot of digital artifacts with the 3.7 lens, while GCam, although less zoomed in, doesn't have any significant artifacts.