Though I do not use these tools any more, I happily submitted PDF written in org-mode (then converted to LaTeX) instead of GUI document editor with a close to binary (in readability) file format. It was easy with org mode, but I did not have to do anything complex. Configuring LaTeX for emacs and editing the generated document by hand might not be enjoyable.

I also wrote html directly and this was pretty easy, as html + css looks like to be made to write documents (think of CSS float, perfect to put an image in between text) and this was not actually painful, it is not centering div according to grandparent or JQuery debugging...

Then there's Troff, which is LaTeX counterpart. It has most of what you can expect from LaTeX but have a smaller community.

The popularity of the WWW made html easy to convert to .docx formats, and all the document structure, and maybe even the CSS, is preserved.

You can then write in markdown or anything else, add a .css, and then open it with libreoffice and save it to .docx for submitting it.

Not sure this is as easy with the other two unfortunately...