Hello David,
You make your point very clearly in your essay. There is not much to quarrel with except to make or ask one or two questions or statements.
First, in your description of "physical entities were said to 'exist'", you mentioned the defining properties as mass or energy equivalence. If some measurable locus that was massless, and 'cannot deliver energy', but measurable in the sense that we can say the volume is 100 cubic metres, does it exist? In my opinion and according to Leibniz, I think in his Monadology, the defining property of what exists is the occupation of some locus.
You discussed in some detail the Platonic world, which is the road our mathematics and physics have in the main followed. Historically, there was a fork in the road, which led to the Platonic one and a less favoured one, which I discussed in my 2013 Essay, 'On the road not taken'. Aristotle, Proclus and others opposed the Platonic route with good reasons for doing so. You may take a look.
As you near the end of your essay, ideas like Frank Wilczek's Grid are introduced as a possible replacement to the old ideas of aether, plenum, substance, vacuum, spacetime, or world-stuff. If the Platonic route was followed but in a questioning rather than unquestioning manner perhaps there would have been no need now for this search for a replacement, as Space itself would have been able to do the job, with the smallest units of the grid being the non-zero dimensional point. This is the focus of my essay this year, essentially a continuation from the theme of the 2013 essay.
You may wish to read and comment. Thanks.
All the best in the competition.
Akinbo