While I'm not arguing with the way the "tests" were performed as to the question of image size vs. pixel size, my experience in this has given me some reasons for going with the image size crowd.
I was a partner in a commercial photo lab here in New york for many years, and have seen mucho photo's come through, in addition to my own early work in fashion and advertising. The one thing I've seen time and again, is that the final image size is the thing. Whether using film or digital, it must be sized to the final purpose.
In regards to that, and the medium used, we see the differences in format, and sensor size, and rez. The same for film. ISO, obviously plays a very big part.
An 11 x 17 two page mag spread will remain the same regardless of the original medium used. The same of a gallery print.
Assuming the lenses are capable of resolving close to the limit of the film or sensor, the rez of the medium will be a determining factor. This, I have seen, affects noise as well. What I have found is that, talking about digital (though film is similar), a sensor with significantly higher rez, assuming equal noise at equal final pixel size, shows less apparent noise on the image. The reason is simple, the pixels are much smaller, and the noise is therefore finer, and less observable. Since we purpose our images for a specific image size, that's what really matters in the real world.
Of course, if one is a "cropper" things may come out differently.
But, otherwise, it's like printing a 16 x 20 of an ISO 100 film vs printing it from a 400 ISO film. If the 100 film grain is enlarged to equal that of the 400 film, the "noise" may be about the same, but for the same image size, the 100 film will have the lower noise, and greater sharpness.
I realize there are various ways of looking at this question, but I've never seen anyone print to the grain size for any normal work. The medium chosen is usually that which will give the required quality at the needed image size.