Just looking at their WP48 young has been much the better performer over their careers.
However there is an interesting point. Young's numbers get better the more minutes per season he plays. This is the opposite of most other bench players. Maybe that means his worst performances will come early in the season and he will improve as he plays. Considering last night's performance he had better if he expects to stick with the Spurs.
BTW, the Spurs can sign a player for the 15th spot and still have their flexibility by signing the player to a non-guaranteed contract. This is useful if they want to take an extended look at someone.