If I were to make my own generator from scratch, I'd go with python. It's the language I work with the most. A lot of my blog content will be generated from python (figures etc) or will show python code. So having a site generator in the same language can help me add features by hacking on the generator code in a way that a single binary cannot.
I migrated from Pelican (Python) to Zola (Rust) because of the ease of replication of the environment. After a few years it was a pain to recreate my pelican environment and even the tools I'd used to try make that situation easier (pipenv) were undergoing their own bitrot.
I went with Hugo too. I used Gatsby in the past, but it was slower and it felt a bit odd using GraphQL in the way it does. Maybe that'd make more sense if I was using an API to deliver content, but for simple markdown pages, it seemed unnecessary.
On the other hand, having single binary is good because you don't have to install the runtime to tinker with the tool. Yet I do agree that tinkering options are very limited in comparison.
If I were to make my own generator from scratch, I'd go with python. It's the language I work with the most. A lot of my blog content will be generated from python (figures etc) or will show python code. So having a site generator in the same language can help me add features by hacking on the generator code in a way that a single binary cannot.