My markdown file format is really simple too

In what way is formatting more complex with HTTP? Assuming the mime mappings are set up correctly the HTTP server pushes out the files with the correct content type and with that you can edit your text files with ed for all I care and it will work. The fact that you can do more complex things with HTTP does not mean you should, the aforementioned example of a directory full of files is just as valid as it was when Tim Berners-Lee fired up the first site on his Next cube.

What special tools? Since when is vim a special tool? What special file format? Special file formats exist but none are required. I don't see an answer to the question here.

No it's not. That is entirely a choice. My website is just HTML files in directories with other files. The html is handwritten and just <p> and <ul> and the like. I just use a normal text editor.

Gemini is not simpler than HTTP/1.1 and writing HTML. Gemini is like forcing yourself to write in Haiku because it constrains you rather than just limiting yourself ... yourself.