Yes, it is. The same principle holds.
Except that all grains are the same size, whether they belong to a sheet of 4*5 Provia, or to a 24*36 roll of the same film.
Pixel size does obviously differ.
The only question really is "are the lenses able to pass enough information for the sensor photosites for these sites to be able to collect enough quality image information". This should be done at equal pixel count.
The theory says that so-called FF sensor should do this better than APS sensors when resolution reaches a certain level. I can relate to that.
You are saying that this limit has been reached with current generation DSLR, I am saying that I haven't seen any experimental results showing this. I am not even factoring DoF/diffraction in the equation, but this would further level the playing field.
Science is based on the usage of experiment to back up theory. I see the theory, but I don't see the experimental results backing it up.
Even in this Canon dominated world we live in ( ), nobody has been able to come up with a clear demonstration that - at low ISO - a 1ds2 file looks better on screen - or prints better than a D2x file.
I understand that some people might not be interested in this discussion, but if you engage in claiming that one system is better than the other, you owe to intellectual fairness to check both. I did and couldn't see an advantage to FF in terms of actual resolution.
Again, I am not denying the value of FF in terms of high ISO noise and DR and I fully understand that some people see these aspects to be important enough to select FF. I will probably do the same when Nikon releases a FF body. What I cannot accept is the selection of FF on the un-proven assumption that it delivers sharper images.