The Referee suggests adding a plot simply because the paper does not contain a single plot. The Referee did not suggest that some specific information in the paper could be better presented using a plot. This is not useful feedback for a technical paper. You can respond by saying that you did consider adding a few plots, detailing exactly where in the paper, but that you ended up deciding against doing that, and then explaining why on balance the plot would make the paper worse.
What matters is that you can explain that the content of the paper is what it is for good reasons. So, plots are not included, not because you are too lazy to bother making plots that would likely make the paper a lot better, but rather because it would actually make the paper worse.
Technical papers don't need to look attractive, you don't need to catch the attention of readers using nice-looking figures and plots. It's unfortunate that there is now a trend where people do include figures for the wrong reasons in technical papers. Editors of journals don't act against this because figures add to the publication charges, particularly color figures.
Your audience are researchers who want to read your paper for the technical information contained in it. It's then best that the information is presented in a form that's most appropriate for them. If a plot were useful, then you would likely already have included a plot in your paper. If a potential reader would not have read your paper just because it doesn't contain a plot then obviously that reader is not doing serious research for which he/she needs to read your paper.
The logic of including plots to catch the attention of readers is therefore only appropriate when you're writing for a wider audience of people who are not directly involved in your research topic, for example in a review paper.