I can’t find a solution to the fremen oppression prior to atreides take over of Arrakis just yet as an idea
It is really a tricky one… unless there is some sort of fremen text or something that could be quoted about the Harkonnen rule of Arrakis and express a hatred of them instead of the dedication to fredrico deLaurentis at the very start I honestly can’t think of a place to handle this or how to begin to sow that thread.