Asciidoctor PDF works as long as you are ok with what you could call the general "template" it uses. You can modify details within that, but if you want to change it, other approaches are required. Last time I had to deal with it I went with DocBook5 and then used a conversion to LaTeX to "break out". I agree with the asciidoctor guys about not offering more flexibility with that "template"; they have other things to focus on and it works well for cases where no specific layout is required.

I have written several books. I used Markdown for the first one.

Then someone recommended AsciiDoc and AsciiDoctor. It was a much better experience compared to Markdown. Sure, not for pixel perfect tweaking. Still enough parameters to play with. Easy to create PDFs and EPUBs.

I like asciidoctor because it is a text file and easy to version control, I have written couple of books with it and made into pdf, but I am still looking for actively maintained themes, so for self publishing and KDP, I am using pandoc and bunch of tools to convert it into various formats(docbook, md, docx etc). My current workflow is convert into docx which is imported in kindle create and optimise it with kindle previewer.