Yes, you guys call 'useable toanlity' 'sensor DR', I have never understood that to be a way of stating 'photographic DR', I only know and understand the difference in recordable luminosity values.
Again, I think this is an area where the technologists have confounded and annoyed the photographers. When I, and millions of others, think of photographic DR we are thinking about the difference in scene luminosity we can actually record, not the point at which the dark tones become noisy. Replicating that capability on devices with a much smaller luminosity range is not and never has been the question.
So who has some RAW step wedge files to upload?
But 'the difference in scene luminosity we can actually record' is exactly what DxO is measuring. Because their DR is defined as the brightest bright vs. the darkest dark that is not lost in noise. 'Not lost in noise' is where SNR = 1, according to DxO. This is known as 'engineering dynamic range'.
Would you like DxO's lower cutoff to be higher, since you can't use SNR = 1 (where tones are completely lost to noise)?
SNR = 1 is used as the lower cutoff b/c different folks could argue till the cows come home what SNR is usable.
If that's what bugs you, then use Bill Claff's excellent analyses, where he defines a 'photographic DR' using a higher SNR cutoff:
The differences between cameras are still fairly similar to DxO's findings, but the absolute numbers are different. Higher SNR cutoffs on the low end tend to shrink the differences between cameras of the same sensor size. After a certain point, a higher SNR cutoff won't even distinguish between cameras of similar sensor sizes, b/c the lower SNR cutoff will be dominated by the effects of shot noise (which'll be similar between cameras of similar sensor sizes), so that's not helpful either.
But Bill Claff's results vs. DxO's normalized results is just half a stop different (2.5 EV vs 3 EV) for the D810 vs. 5D3 for example. Not exactly earth shattering.
Is that what this entire debate, and all this arguing, is actually about in the end?