The Chiefs run the ball less than any team in the NFL. Their pass to rush ratio is by far #1 in the league (and one of the highest in the history of the league). They also lost Kareem Hunt, and actually got better.
The 49ers are using an undrafted running back who was cut by 7 different teams in his short career. If he were actually that good, and not just a replaceable cog in a scheme, one of those 7 teams that cut him would have realized his worth.
Running backs are completely fungible, and anyone who thinks you should invest heavy resources into them (whether it by with high draft picks or a big long term deal), has no grasp of how to build a team.