This isn't a track meet. Those guys can rake.
The problem is avoiding double plays, going from first to third and scoring from second on a single. There are specific things that making the team slower makes it more difficult to do.
Adding Zimmerman and subtracting Harper or Cabrera or even LaRoche, probably, makes the team slower.
Ramos, LaRoche and Zimmerman just happens to be the worst mix as far as speed goes.