You are right of course. There is still nginx taking care of everything. The point is that you need nothing but nginx/caddy/Apache.
Currently, I don't know any way how to initiate execution of scripts over http server so there is a systemd timer checking changes in files and recompiling the whole site. This has lot of downsides. The easiest would be if the static generator reacts on existence of a specific file - recompiles the site and removes the file afterwards.
Maybe check out the https://vlang.io. It might be similar to what you are doing and personally I admire the ideas and decisions the author made so far.
I am working on a blogging platform that does not need any backend (in terms of an app listening for http connections). The overall architecture is an web app that is talking to WebDAV and then pages get build by a static site generator. I use getpelican.com but you can use Hugo or Jekyll based on your preference.
Currently, I don't know any way how to initiate execution of scripts over http server so there is a systemd timer checking changes in files and recompiling the whole site. This has lot of downsides. The easiest would be if the static generator reacts on existence of a specific file - recompiles the site and removes the file afterwards.