Font sizes for headings across all Stack Exchange sites is garish and significantly overstated, giving an amateurish look to questions that use headings where they would otherwise be quite appropriate.
For example this answer uses quite semantically appropriate h2 tags (via ##) and yet it presents horribly. I know I have tried using h1 and h2 before and just switch to bold or bold+underline for this very reason.
Can h1 and h2 within question and answer text be mapped to be just bold plus a slight increase in size over the base text size, say 2 points and 1 point respectively, and perhaps h3 to bold+underline.
And, secondarily, perhaps the remaining heading values should be do-nothing (and reserved for future use).