I feel that Joe Sr. was looking for a pretty, agreeable, and stupid wife who would be nice arm-candy for JFK in his pursuit of the Presidency.
He found all that in Jackie
You’re underestimating Jackie. I think they saw her as a way into a higher social standing.
Before she met/married Jack she was a cub reporter whose first assignment was to do a piece on the sole burlesque house in DC, the Gayety Theater. She made the visit, did the interview and then got engaged and quit. Don’t recall if the piece was ever published. But a deep web search will find an item about her reporting career start.