OK, well here is 100%. The fact is there is just no difference.
Sporgon, I'm a little confused by what you are trying to show here. If you are saying that you can crop a full frame sensor image to the same effective focal length of an uncropped APS-C camera and not lose any significant detail, I don't think most people disagree with that.
When you have to do extensive cropping, sooner or later, the full frame image taken from the same spot with a sensor of equal megapixels is going to deteriorate, simply because the final image has less resolution.
I think this is the point of contention.
Yeah, sure if you don't have to crop severely, the "reach" advantage of a crop sensor may not be significant. But, if you must do some significant cropping of the image, the greater pixel density of the APS-C sensor will hold up longer.
Your experiment is a little unfair, because you are using a 12 mp APS-C sensor. A more fair comparison would be to take a 70 D and a 6 D, which are fairly close in the number of megapixels. Shoot the same scene with both from the same spot. Crop the 6D image to match the framing of the 70 D and then keep cropping away until one image deteriorates to the point where it becomes unusable.
Logic would suggest that the 6D image will fall apart sooner, because you are starting with less resolution. But, it would be interesting to see if that is really the case.
Of course, it if turns out the the fall apart equally, despite the difference in resolution, then all those people clamoring for a high-resolution Canon full frame camera would have to rethink their demands.
Frankly, I'm okay with either result. I would just suggest a more fair comparison.