Even though I made the original post about the FAA viewpoint I agree that we should not necessarily take their viewpoint, or anyone else’s as definitive. The main reason for making the post was to show that there are differing views on the “correct” answer.
I believe that we make life too complicated for students by concentrating on the difference between primary and secondary instruments and also between control and performance instruments. Surely the most important thing is the totality of information that can be gained from the combination of all of the instruments. At the initial stages of teaching instrument flying the student is taught to scan the instruments since they require some basis for instrument flying but I concur with Cat Driver that once we gain experience we subconsciously assimilate information from the instruments rather than formally scanning them.
When teaching IMC students I find it interesting to note the improvement in the student’s full panel flying after they have been taught limited/partial panel flying. I suspect that this arises because the student is starting ,at least to a small degree, to assimilate the data that is being provided by all of the instruments and is using that data to achieve the desired result rather than slavishly following a rigid scan.