There are at least two compelling advantages of DxOMark here -- one is the simple practical one -- as we do not have access to Canon's internal processes, we can't use their internal benchmarking results to appraise the 1DX or compare it to competing products (again, assuming Canon have an internal testing regimen, one would expect that they would run all of their own, and several competing products through it).
Second, even if we could see those results, it would be misleading to compare cameras that had been tuned to those specific testing processes with those that hadn't (basically, it would be analogous to in-sample versus out-of-sample testing)
Ultimately, real world results are what counts, yes? Photographers buy cameras to capture images, not to pass specific testing processes or specific testing regimes, ya?
So, can you point out specific real world scenarios that Canon's cameras perform really well, outside of what DXOMark can ever reveal? Perhaps Canon's internal test regimes are tailored for such instances?
To address your first question(s) --
I'm not sure what you think you're disagreeing with. Better equipment helps us get "real world results", and the sensor is a key part (but not all of) our camera equipment. Photographers have gotten great results before the latest sensors were available, indeed, before digital was available.
If you're happy to use the same equipment that produced great results for photographers who didn't have access to the latest gear, then you have absolutely no need to pursue the latest technology.
However, if you are in the market for the best technology the market has to offer, benchmark results count.
You can wait until the technology in question has an established track record, to see which products get the best "real world results" but there are least two problems with this -- one is that by the time this established track record is realized, it is not the latest tech any more.
The other is that "real world results" depend more on the skill of the photographer than the technology. You can buy the same equipment used by the photographer produces the greatest "real world results", but the photographers talent does not come in the box with the equipment.
In answer to your second question, DxOMark only test sensors. The camera is much more than a sensor. Canon almost certainly include considerable testing of features including but not limited to ergonomics, durability (weather proofing and longevity). and autofocus performance. And there are yet other factors that can't really be tested, but are important all the same -- Canon's unique ability and willingness to stand behind their products. This is a combination of a first rate support system, and complete control over their product line. For example, there is no other full format DSLR manufacturer that completely manage their product development (cameras, sensors, lenses). Nikon's performance numbers are impressive but one could reasonably doubt Sony's
commitment to Nikon's
DSLR line. Nobody doubts Canon's commitment to Canon. Canon's strategic decision to avoid taking the easy way out and just buying the sensor might seem to hurt them in the short run, but it is a strategic decision that takes the long view.