Even if the DO's influence is keeping the trollocs in check (ie keeping them too fearful to be lazy, keeping them from deserting, and the other things that are usually done through their fear of the Fades), someone still has to direct them in battle; keeping tabs on the dispositions of the fists, directing units on the march and on the field, and all the other small-scale administration that is usually done by the Fades. The DO can't relay orders direct to the trollocs without a middleman, unless he's invented mind to mind communication. Which I doubt or else he would have won already.

This means that without sufficient Myrdraals, then BA or Forsaken (or other channelling DFs) are going to have to be told off to control the trollocs during battle. Which means that the DO's channelling forces are going to be dispersed, at least partially, rather than all in a single massive group. Which is good news for the Lightsiders, if true.