That’s understandable. Maybe try commenting out all the generating code and adding it back piece by piece until the document size balloons, then you’ve found your culprit.
The MuPDF ‘mutool’ is pretty handy for dumping internal PDF content to see which parts are large.
I dont really want to turn entire document into svg. There’s some text, some tables, things that fit perfectly for HTML and not so much for SVG.
Right now I’m thinking about using GNU groff. It would be a very different approach.