I cannot imagine a more pointless, unrealistic test. If your goal is to demonstrate a passion for creating the ultimate rig for imaging newspapers taped to brick walls, congratulations, you've succeeded. But if your goal was to demonstrate an understanding of actual photography as practiced by actual photographers....
Again, the test I performed resulted in two images with the same number of pixels in addition to the same perspective and depth of field and background magnification and out-of-focus blur and everything else a photographer cares about. The only variable was format size, and we saw that sharpness is very closely related to format size and not at all related to the number of pixels in the image. All your test demonstrates is that, if you ignore everything that actually defines what an image of anything other than a test chart looks like, you can get two systems with certain similar specifications to make similar images of a test chart and nothing else.
Therein lies your problem. Your test attempted to compare 'the same picture'. You might
have a point...if that were the goal. But we're not asking about 'everything that defines an image', we're asking about only one thing. Let's revisit the title of this thread: Is FF sharper than APS-C?
Not 'does FF take a better picture'. Yes, photographers care about 'better pictures' but that's not what's being asked here. Only sharpness. So in this case, taking pictures of a newspaper taped to a brick wall would be a far more appropriate test of the question than yours.
"The only variable was format size..." Really? Do you understand what a variable is? Do you know the difference between a dependent variable and an independent variable, and how to tell when a dependent variable becomes a confounding variable? You used different lenses to take the different pictures. You processed the images differently. We call those confounding dependent variables. Your test was not designed to answer the question, and therefore was flawed for the purpose at hand.
"...the test I performed resulted in two images with the same number of pixels in addition to the same perspective and depth of field and background magnification and out-of-focus blur..." Guess what? So did the TDP comparison I linked. Same number of pixels (but achieved without
scaling), same effective perspective (indeterminate because the image has no depth), same effective depth of field (essentially none, as the entire subject is within it), same background magnification (none, no background), same OOF blur (none, everything in focus). Unlike your test, the TDP ISO 12233 crop holds everything constant. It's no accident they're called that - ISO 12233 is the "standard for measuring the resolution of electronic still imaging," and that's what we're talking about here...not 'better picture', sharpness
An analogy: It's as if I asked, "What is the sodium content of french fries vs. carrot sticks?" Your test is trying to answer a question like 'which one tastes better?'' Yes, that's an important question for a person who wants a snack, but that's not what's being asked
. I'm looking for a chemical analysis of Na+
content, and you are conducting a blind taste test. Interesting and informative, perhaps, but a complete fail as far as answering my question.
If you want to test the effect of sensor format on sharpness, you must hold everything else constant - especially the lens and the post processing. You varied both. It's not that your test was invalid per se, but rather that it was not designed to address the question being asked. Sharpness is just one component of picture quality, but again - that's the one we want to test.