I think that DxO does the photographic world a great disservice by claiming to test sensors when they actually test the entire chain. Lots of folks get very confused.
The disservice done by DxO is in the reduction of their measurements to Scores which are biased and determined in an undisclosed manner.
What good would it do to test the sensor and ADC separately? If the sensor is good and the ADC is poor, it's not as if I can just pop a better ADC into my camera. Testing anything but the 'entire chain' would have no real-world utility (except fueling speculation about what might or might not be possible at some unspecified future time).
I am not proposing that they test the sensor and ADC separately, they could not do that without opening the box and connecting equipment and that we would really be difficult in the case of Sony. What I am saying is that they are not really reporting sensor performance, they are reporting camera performance and should say so.
The title of this thread "Can Canon deliver a sensor that is truly class leading" is ample proof that a problem exists with people's understanding of this matter. Once you take the time to figure out how the cameras work and take the time and study the DxO data (particularly as digested by sensorgen), It becomes quite clear what is going on. What it all says is that Canon's sensor implementation is performing just as well as Sony's it is just that the camera implementation that they chose (and for some reason seem to be sticking with) does not perform as well in this one particular parameter.
I think that we can all agree that the end of the day, photographers take pictures with cameras and not "sensors" and Sony has managed to get 14 bits of DR out of a 14 to 15 bit sensor while Canon has only managed to squeak 12.5 out of theirs. But it still appears to be a sensor that is quiet enough to produce over 14 bits of DR. So IMO, to say that Canon's sensor itself is sub standard is simply not true, and the measurements (even those of DxO do not support that statement).
BTW: you are spot on WRT your other comment about DxO's summary scores -- a total crock of crap IMO.