In essence what you are saying is that there's no point to increasing focal length. A 400/5.6 is no better than a 70-200/2.8 according to you. They have the same aperture, and similar optical quality, and an increase in focal length is exactly the same thing as a decrease in pixel size as far as resolving power goes.
Of course, you're just wrong.
No, that is absolutely not what I am saying.
What I am saying is 'in same generation sensors the differences between a crop camera, and cropping a ff camera to get the same fov, especially appropriate in focal length limited situations, shows negligible difference in resolution even in ideal situations'. You can only test this with same (or very close) generation sensors, 6D and 7D MkII would be valid, 5D MkII and 7D would be valid, etc etc, if you don't have two same generation sensors you cannot test this and any 'illustrations' are entirely bogus, as all yours have been when we have danced this dance previously. Specifically in this thread I am referencing a 7D MkII and current FF Canon cameras, the 6D, 5D MkIII and 1DX, now obviously none of us have a 7D MkII yet, but when we do I am fairly sure we will see the same thing.
So, same lens, same place, same subject magnification, crop ff to crop camera framing and look at the difference, exactly as I illustrated above, when you do that in realistic enlargements there is no visible difference, when you take enlargement up to well over 100%, as my crops do, the differences are just visible. The crop camera has slightly more resolution and more noise, if you mitigate the noise you lose the detail, if you sharpen the FF you get more noise, if you normalise them it is a wash even at these extreme enlargements.
This has been true for several generations of sensors and I tested it myself because I wanted a 7D, but after doing this chose to not get one. Now I would hope a 7D MkII would show an improvement over the MkI results, but it looks like I'd still be better off getting a 1D MkIV !
It is funny, I have had this similar conversation here several times, normally with people who don't own both, they argue endlessly about the 'resolving power' of the crop camera, the 'pixels on target advantage' etc, invariably when they get a FF camera they too don't see much difference.
Neuro, who used to own the 5D MkII and 7D, sold the 7D after getting his 1DX and doing similar tests, AlanF used to categorically state the difference was massive until he got his 5D MkIII and on and on............
Show me some 5D MkIII-7D MkII, or 5D MkII-7D >100% crops using the same lens from the same place to prove I am wrong, and my 1Ds MkIII and 7D crops which illustrate my specific point perfectly are also wrong.