If the 5ball is involved one of the players is NOT world-class or even close to it. KM must have been high when he told you that. He MIGHT give it up IF he got ALL the breaks but even then i seriously doubt it.
When a world class player gets an open shot in 9 ball, you can basically write off the rack. It doesn’t matter if he gets to stop at the 5 or the 7,8,9...most of the time. And if someone like mccready is running racks it doesn’t matter what ball he gave you as a spot. I can definitely see him giving people the 5 to get them to the table, even his contemporaries.