I have now seen the video of the derby. I was interested in seeing how many times United chose to find Doyle or Montgomery in central midfield, followed by them successfully finding a teammate. This happened four times over the 79 minutes they played together:
13:20 Lowton throws the ball in to Doyle. He finds Quinn with a long pass.
36:50 Evans lays it back to Doyle, who plays it back to Evans.
55:10 Lowton throws it to Doyle, gets it back.
75:44 Jean-Francois throws it to Doyle, who returns it.
So that's the complete playmaking from central midfield in nearly a full game. Coming short for three throw ins, and one short lay off.
I think this suggests that this pairing leaves the creativity and attacking responsibility to other players. It may be enough against the poorer sides in this division, but I don't think it's a good enough solution in the long run.