Maybe a fix for this would be to style chapter TOCs in some way that makes it clear that they are TOCs -- for example, add a (subtly) visible bounding box, or something. Or maybe if a chapter has a single section, just do not print the TOC at all. I have no idea how to implement such a fix, or whether it'd be really acceptable after all.
Or move 4 paragraphs of introductory material into its own section so that there are two sections and a brief sentence for an intro.
I don't see a special case for a single section to be a productive use of time. Improved formatting overall for the chapter ToC has merit.