I recently stopped using a static site generator for my personal site [1] in favor of just manually maintaining a bunch of HTML files, for similar reasons. The last straw for me was a nonpassive change to the site generator mysteriously breaking the homepage. Themes are frustrating as well since they either constrain you or force you to spend time figuring out how to shoehorn what you want into the theme. I only post occasionally, and keeping all the pages consistent with each other isn't as important to me as being able to post a page that looks however I want it to with minimal hassle.
I did something along those lines once, but I used https://github.com/susam/mdme as the preamble so I could write the posts in markdown rather than html. The index was an extra line to add links to index.html.
[1] https://brokensandals.net/