After all the comments about F'drun in the 'Threadfall' story, it only took that one scene to get the mettle of the , ahem, man.
Bad decision that. Out of D'gar or M'rell, both of whom had been de facto wingseconds for almost the entirety of the last Fall, R'feem knows he can trust and count on D'gar. Regardless of who or what the 'new guys' were, R'feem doesn't know them from Adam. Add to that, two new (and untested - in this wing) wingseconds into an existing wing... well, I can only see chaos at this point.