Well he's picked the right moment, as Cindy and Cathy have pretty much 'incapacitated' each other, so all he has to do is stick up Deb with the revolver while he saws through the rope with his left hand and Barb thumps down onto the floor. This will take longer than the movie style scenes of 'ropes always come apart instantly when touched by blades' but it'll be over before Cindy & Cathy are ready to do anything about it
That way he avoids the situation of having to keep three opponents under control, at very close quarters literally within arm's reach, while at the same time trying to concentrate on sawing down a swinging victim from her rope. That would have been a recipe for disaster