Dear Steven P Sax,
From what you have stated, I interpret your 'physical reality' as follows: From observations to explanations to mathematical relations to correct predictions, such a sequence gives us some idea, and from the mathematical relations (that make correct predictions) back to observations and explanations, the reverse sequence helps to fine-tune that idea, and thus we can arrive at the physical reality. There are no pre-assumptions regarding reality.
That is exactly what I meant by the term 'mathematicalism'. As pointed out in the example in my essay (the case of A and B drifting apart), observation, explanation, mathematical relation and prediction perfectly agree, but still it is impossible to arrive at the underlying 'physical reality', because there are multiple options and we have to select one. Physicalism implies that there should be a pre-assumption that reality agrees with our commonsense ideas (about the 'basics').
I propose that light contains streams of fundamental particles moving along spiraling paths, and so it exhibits wave-nature also. The particles are further quantized into well separated physical units (quanta) having a fixed length. A 'quantum' is a thus real physical entity having internal structure. What I oppose is the dual-nature, especially, the 'instantaneity' of the dual nature; light is not an electromagnetic wave; it is particles having variable electromagnetic filed. The 'physical reality' implied by QM is incorrect, though the rest of it (its role as a mathematical tool) are correct.
Superposition is instantaneous; it is not 'body alternating between two positions', or 'body alternating between two forms' or 'two bodies alternately occupying the same position'; it is like the Schrodinger's cat being alive and dead at the same instant. It goes against physical reality. However I agree with your argument that in the 'present circumstances', 'proposing superposition' has some validity.
Let us do the 'one-slit' and 'two-slits' experiments using tennis balls instead of electrons, the sizes of the source, the slits, the gap between the slits, the thickness of the material in which the slits are made and also the distance between source and slit magnified proportionately. Now throwing the balls from all possible positions in the source, in all possible directions, we will get interference patterns in two-slits experiment, but not in a one-slit experiment. Here, there is no superposition, there is only close-stacking. Can you say the tennis ball has a dual-nature based on this?