Lots of backs can get a couple of tough yards consistently. It's nothing special. I never said he sucked. He is just so over-rated. People talk about him like he is adrian peterson. I don't really have the time to look it up right now, but I will bet that the list of backs with more than 1 1,000 yard season over the past 7 or 8 years is pretty unimpressive.
The problem with the amazing season that you referred to is that the durability that you noted didn't apply that year. He had a nice stretch during that season, but his body didn't hold up. How about the next year (maybe 2 years later)? More injury issues, but most of all, he had a massive case of the fumbles which hurt the team.
Last year, not even the leading rusher on this team. Do you think teams really game planned for jackson? Of course they didn't. They were focused on shutting down spiller because he was the only guy on the entire offense who was capable of killing a defense. Do you really think that defenses were afraid of fred's extra 2 or 3 yards when we had no passing attack and only one real weapon?