Your analysis does not jive with my understanding of DSP at all. I am not an expert at camera sensors so I won't provide an alternative explanation, but I do not believe your math is properly applied here practically.
My understanding, and it's been nearly a decade since I did this stuff in school is that you've got 14 bits therefore 16,384 possible brightness levels.
Each stop of brightness has twice as much light as the previous.
So the top stop in your exposure will have 8192 levels in it, stop 2 will have 4096, then 2048, then 1024 then stop 5 will have 512 levels. You can see where this is going, but stop 10 will only have 8 levels in it - while there is value to those levels being smooth, there is a pretty fundamental problem when it comes to using them to extract detail.
Now if dxo are downsampling the image then that helps some. If you've got 4 pixels going into one, then I think (if I recall correctly) that gives you an extra 2 bits of usable range.
This is where HDR shines. If you do a +2, 0, -2 HDR bracket - you have 8192 levels in stop 1, 4096 levels in stop 2, 10240 levels in stop 3, 5120 levels in stop 4, 10752 levels in stop 5, 5376 levels in stop 6, 2688 levels in stop 7, 1344 levels in stop 8, 672 levels in stop 9, 336 levels in stop 10, 168 levels in stop 11 and so on...
Search for ETTR for more discussion on this.