Asking whether radio waves really count as light is just arguing a definition. That's not interesting to anyone who understands the underlying physics.

Notice that the questions he gives for essentialists are actually interesting questions, they're just imprecisely phrased, e.g. "what is matter?" These questions were asked before we'd decided matter was atoms. They were valid questions and serious scientists treated them. Now these questions are silly because we've already solved them and moved on to deeper questions, like "where do these masses come from?" and "how will the universe end?"

When a theorist comes up with a new theory they are usually trying to answer one of these essentialist questions. "What is it about antimatter that makes it so rare?" The theorist comes up with a guess, computes some results, spends a year processing LHC data, and realizes that their theory is wrong. At some point in here they switched from essentialist (considering an ideal model) to nominalist (experimental data), but the whole distinction is unnecessary.

... they don't study some abstract platonic version of light or atom derived from our intuitions ...

Yes, they most certainly do. QED is an extremely abstract idea, derived from intuition about how the light we interact with on a classical level behaves. This is called the correspondence principle.

String theorists come up with a theory based entirely on mathematical beauty, much like Plato.