Some poster throw in "post production", that is not a valid arguement either.
The discussion is merely academic apart from post production. Nobody publishes images without post work, or at the very least non-neutral camera settings.
1. For the same pixel count on both formats, both can be as sharp as each other, assuming that the lens can out resolve both sensor in the imaging area. That will put a lot of stress on the lens for APS-C sensor. The lens need 1.6 time reolving power compare to the FF.
This is false. Resolution is not a single number. It's a graphed MTF curve of contrast achieved at ascending resolutions as recorded on the sensor/film. The higher the resolution, the lower the detail contrast or sharpness.
If you have a FF and APS-C sensor with equal pixel counts, and all other factors are equal (lens, scene, etc), then the APS-C sensor will produce an image that is less sharp than the FF sensor. Within its cropped area, it's recording at a higher resolution than the FF sensor, and the lens will deliver less contrast at that higher resolution.
2. There are isolated incident that the APS-C can actually sharper than the FF if the lens use for FF have a severe problem in curvature of field or severe unsharp conrners. Since APS-C snesor only using the center part of the FOV of the lens. These problem may not exist. Therefore the APS-C is actually sharper.
Yes, there are some lenses where this is the case.
3. FF will be sharper if the lens cannot out resolve the APS-C sensor but it will out resolve the FF.
Sort of. Again, resolution is not a hard number. It would be more accurate to say that FF will be sharper than expected (see point 1) if the lens MTF curve favors lower resolutions, i.e. if it really drops towards the bottom of the chart in the region where the APS-C sensor sits.
It should also be noted that contrary to popular belief the vast majority of lenses can out resolve current DSLR pixel pitches at MTF10. You would almost need a coke bottle to fail to do so. If you want to see lens challenging pixel pitches you have to look at compact cameras.
4. There is no doubt that FF will have better picture quality than thre APS-C, due to less noise, better DR.
Way too broad of a statement. There are actually people who will take this to mean that a 1Ds (original) will have better IQ then a 60D or 7D. It won't. Technology is at least as important as sensor surface area (noise) and pixel size (DR). Further, at this stage of technology, there are ISOs where noise is simply a non issue between the two formats.
6. In print, most of the difference will not be obvious due to the printing process.
I would say it's more due to scaling, but agreed.
7. How many people can tell the difference in music between amplifier with 0.01% distotion and amplifier with 0.005 % distortion??
In a double blind study I would be surprised if anyone could.