Julius Jones played in 4 of the 6 wins in 2004.
Browns
5 rushes 16 yards
The defense held Jeff Garcia to a 0.0 passer rating that game and the Browns to 202 yards and 12 points.
Bears
33 rushes 150 yards
Seahawks
30 rushes 198 yards
Commanders
22 rushes 57 yards
The defense held Washington to 223 yards and 10 points
Julius really only contributed to 2 wins that season. They were big games for him and I could see Jackson having similar results in those two games. I can fully envision Jackson helping the team win at least one more game over the full 16 game schedule than what Julius did. If he couldn't then he isn't going to be able to elevate them to SB titles, which is a considerably more difficult task.