When I decided it wasn't worth keeping my personal site dynamic, I took my webapp and pulled out the core of it, and built a small little script that enumerated the possible urls and "requested them" from the old webapp and wrote them to files, turning the webapp into a static site generator.

Yep, exactly. Wget can do this with the --recursive flag.

There are legit services/plugins that do this with Wordpress for similar reasons.

I've been contemplating converting some legacy WP to static, but have not had the time to review available options.

With root access to the server / just good old wget, are there benefits to using the plugins/services? Which would you suggest? Would be grateful if you shared your experience.

Why not varnish then?

Simply because a lot easier to host static files than it is to host a web server binary that has to be executed. I can just upload to GitHub Pages or AWS S3 and let them worry about the HTTP caching, TLS certs, upgrade to HTTP/3, etc.