you can turn it as you like but with f/11 f/16 on 35 and f/22 on MF you get diffraction if the pixels are too smalls, using a lower f-stop is not always what you want or need
Agreed: my points are only that
A. the problem is equally bad in any format, so long as lenses are good enough to give the needed resolution, so it is wrong to offer this as a reason for going to a larger format than 35mm.
B. more pixels still give a clear increase in resolution at lower f-stops, and no decrease in resolution at any f-stop, so it is silly to say that there is no point increasing 35mm format sensor resolution simply because at some choices of f-stop (f/11 and above?), there is not much resolution gain.
As to why it is equally bad in any format (with good enough lenses):
1. The dominant reason for stopping down to an aperture small enough to cause diffraction problems, like your example of f/11 in 35mm, is to get enough DOF.
2. Changing to MF, that same need for DOF requires a higher f-stop: about f/16 in your example.
3. At the different f-stops needed to get the same DOF in the different formats, diffraction hurts resolution just as much.
The hard fact is that pushing resolution to the levels offered by sensors of 20MP and up imposes noticeable limits on the DOF attainable in conjunction with that high resolution, through the f-stops needed to adequately control diffraction, and this happens to a degree which does not depend on the format. I suspect that this will someday set the practical resolution limits for still photography, short of special techniques like DOF stacking. (Stitching does not really help: it just effectively turns a lens for one format into a wider angle lens in a larger format.)
P. S. What about all those giga-pixel images? The ones I have seen are all wide-angle views of distant panoramas, avoiding nearby subjects, which is the easiest case for DOF.