Holt was elite while Jackson was very good. I think there were a lot of seasons Jackson wasn't even a top 10 runningback and typically was somewhere between 6-10.
Holt and Bruce were always top 10 and bordering top 5.
The logic could be used just the opposite that Holt had to share the workload and didn't get the opportunities while Jackson had an offense where he was more a center piece.
What hurts Holt in the Hall of Fame is the year Linehan played him with Torn Cartilage in his knee which shortened his career. that 2006 season was quite an underachieving year for the Rams. Everything fell in the Rams lap, with a weak schedule and very few missed games by the core and ended 8-8 with many of those wins against teams trying to lose to get a better draft pick.