MR is taller than JB, don't know why you think he is quite small.
What problem are people trying to resolve here? Without wishing to put the mockers on it, Bree appears to be resilient, so we need a backup in order to give him a rest or to cover for suspensions, minor knocks. Roerslev is exactly that now that he is back, a backup. If that fails we have other options (except they are now needed as first choice in their best positions, i.e. JWP and Abbott, while Jander and Schlotts/Wood are out). Push comes to shove Fellows can play there, and probably either Manning or Weli. Getting a RB in January in the present situation is likely to be #100 on the priority list.