To be fair, the mid-2000s are fifteen+ years ago, which might as well be a century ago when it comes to both markdown, static site generators, and even the web

To be fair, the mid-2000s are fifteen+ years ago, which might as well be a century ago when it comes to both markdown, static site generators, and even the web in general. I've been through similar pains myself, but not in the last five years: there's been plenty of tooling to strict-format all content prior to starting any conversion, and plenty of tooling to convert from one flavour of markdown to another (although, mind you, sometimes that means converting away from markdown first, then converting that back to your new flavour).