LJ was an absolute beast for two years and Herm Edwards simply rode his back and wore him out to get that 2006 team to the playoffs.
He certainly produced up to his draft status as the third leading rusher in KC history. But like most RBs who carry the ball 750 times in a 2 year period, he hit a wall fast.
Much like WR, you had better references at RB like Ethan Horton, Paul Palmer, Greg Hill or Harvey Williams. But again none were drafted by an organization as good as we are now.