I think that your last point gets to the heart of the question, and you are right that we may never achieve a deeper understanding of light, matter, or gravity;

I think that your last point gets to the heart of the question, and you are right that we may never achieve a deeper understanding of light, matter, or gravity; but that does not mean that a deeper understanding is not desirable, or that we should stop asking the questions. Further, we will never know for certain when we have reached the bounds of our capacity to understand, so I will continue to ask "Yeah, but what strings are?". I always like to keep in mind that 'atom' means 'indivisible' in Greek, and yet we found that bound of knowledge to be surmountable (with debatable consequences). I would also like to be clear that I am not criticizing anyone for making insufficient progress; it is just that there is a lot out there left for us to understand, and not all of it is marginal stuff that's "very big or very small".