Hi my-nick, thanks for the suggestion. In the end I wrote a Python script to convert a text file to PDF with some basic fomatting.
I fully understand the Calibre developers view of PDF. In my case I have an old tablet that works best with PDF so I do a "one time" conversion to PDF when I want to read something, then discard the PDF file. It's mainly my short story collection (many thousands of them!) that I keep as plain text. My books I keep as epub, mostly generated/converted with Calibre.