I think you're mostly right. Herbert worked backward from sand dunes in Oregon to create his Dune universe. He needed reasons for people to look and act and fight in certain ways that would make people interested in reading his work. The Butlerian Jihad was justification for why there was no C3PO. It's why the events were told but never shown.
But it's still interesting to consider why he chose those particular devices.
But it's still interesting to consider why he chose those particular devices.