I don't agree with this.
I know you don't, and you argue my examples when I show them, that is fine, you make your cjhoices for yourself and I'll make mine for me.
But I never questioned system resolution as a concept, I know full well the interplay of the elements within that system. We just come to different conclusions when looking at the images they produce, I don't care a fig for technical theories, just understanding why I see what I see.
Well, the example I've usually seen from you is the 7D vs. the 1D III, and I think your argument usually boils down to the fact that the AA filter on the 7D is fairly strong, thus diminishing the value of the 7D. I won't deny that a strong AA filter throws another factor into the mix, and it is a factor to take into account when actually measuring different devices. Even so, the use, or not, of an AA filter isn't a reason to stop pushing megapixel count/spatial resolution. My theory always assumes "all else being equal"...in which case the AA filter would be tuned to provide similar results around nyquist for any given sensor resolution.
I don't deny that it is important to use empirical data as well, however empirical data can and is often interpreted differently. It's a subjective measure, and how the data is interpreted, according to what criteria, and by whom, are all important factors in normalizing empirical results. Personally, I see a meaningful, if not "ideal", improvement in resolution with the 7D over the 1D III in your past visual examples, you do not... That is an important discrepancy, and just because the data is yours does not inherently invalidate the observations of others. I have very good 20/10 vision with my corrective lenses, and perhaps that plays a role. If the 7D had a weaker AA filter, the difference would likely be even more pronounced. One could also perform a test with the AA filter removed from both cameras (thus eliminating the additional factor), and I think the difference in spatial resolution would be quite clear in that case.
Your argument is usually perceptual (subjective), where as I try to make mine objective. Perceptual/subjective arguments, while not invalid, are hard to use as a viable basis for comparison because of the very fact that they can be interpreted differently in the absence of normalization. You see the 7D as having no visual benefit over the 1D III...I see the 7D as indeed having a visible benefit over the 1D III, if not quite as much as theory would have predicted...all using the exact same source images that you yourself produce. That is a war neither of us will win, and one which doesn't help anyone else understand the fundamental value of having a higher resolution sensor.
A 24mp APS-C sensor would arguably demonstrate an even greater lead over the 1D III...I'd be very curious to see you perform a visual comparison of say a D7100 vs. the 1D III, or even the 5D III that was identical to your test of the 7D and 1D III. I'd wager the D7100 clearly outperforms either Canon camera in the realm of final resolving power (spatial resolution).
I'm sorry if my replies frustrate you, but you often seem to be making the (subjectively based) argument that there is no value whatsoever
to increasing megapixel count beyond the point where Canon currently is (~20mp APS-C, ~24mp FF). From an objective
standpoint, there most definitely is, and I think it is important that people understand that. All else being equal, you don't lose anything
by moving to a higher resolution sensor, and in fact
you almost always gain something
Subjectively, images from the D800 (at least at lower ISO/in good light) are superior, often vastly superior, to anything that you can get out of any Canon camera on the market right now. As a Canon fan, I don't really like to give a bone to the competition, but in this case, both subjectively and objectively, a higher resolution sensor most definitely has something to offer...and in a clearly visible, empirical way.