Basic physic is all you need to understand this question.

To skid you unweight the rear wheel, decreasing the amount of friction the wheel can deal with before skidding. Skidding is less efficient for stopping than rolling at just barely less force than is required to skid.

The act of slowing the bike down causes the bike to want to rotate(think clamping down hard on the front brake). If your stopping action is coming from the rear wheel that is the pivot, so the bike and rider's weight are further forced onto the front wheel. Again, less force on the rear wheel provides for less friction.

The conclusion of those is that you will not get the same braking power whether you resist pedal or skip/skid.

IF you were able to resist pedal with a perfectly stable force the entire way through the pedal stroke(especially at the dead spots) AND do this while you put your weight over the rear wheel as much possible, then you could get better braking power, but not as much as even a single front brake.

That said, in my opinion the people who seem to ride faster brakeless probably do so for reasons of both skill and a desire not to have to deal with resisting or skidding if it can be avoided, so the overall average speed stays higher because there is less intermittent slowing down.