I had a go at pandoc when I was writing my (social science) PhD, but I gave up and went back to just doing it all in LaTeX fairly quickly.

From memory the compile times didn't worry me at all. What did worry me was making it look like I'd put far more effort into documentation presentation than I actually had. Which worked well for me, especially big shout out to the hyperref package to get my far-too-many acronyms linked back to the acronym definition table for every mention), links to every citation, and proper links inside the document to each section /page reference.

Then on top of that my hacked together proofreading tools in emacs, and a torturous 10k word chapter 2 to sideline a difficult politicical problem, and I passed first time!

In use cases like the Markdown to PDF pipeline described in the article, sure! Documents there are also simple enough so that compile times aren't too much of a problem.

However, many of the documents we like to set in TeX are more complex than that: bibliographies, figure placement, special typographical flourishes.... And here is where the complexity of LaTeX and its macros adds to the inherent complexity of what we are trying to accomplish (and compile times quickly ballon again).

So, sometimes it helps...?