Let's look at that whole momentum and applied force for a moment. Read any advanced bump skiing thread on here, and you will likely find Bob B's animation with the "back peddling" move. As the skis go from crest through the trough, prior to impacting the uphill side of the bump, the skis, feet, and legs are moved forward. Momentum is being transferred from upper body to the legs. When the skis contact the bump, even if the skier does not actively resist with his leg muscles during that time, their momentum is being reduced by the impulse as the skis contact the bump. No active muscle movement required; momentum transfer has effectively been spread out by the initial back peddling move to include the entire time of skiing, smooth and seemingly effortless. Even if you don't resist at the bump, your legs are loosing momentum, extra momentum that you put into them. There, now the physics matches the reality.
That impulse is pressure resistance. But you are right its possible to be stacked at the moment of first hitting the face of the bump so that a large impulse of pressure does not have to involve so much muscle work. That means most of the speed reduction happens before flexing under that scenario. Momentum of the CoM is what matters here, back pedaling changes your states of balance, but unless it contributes to resistance and pressure its not changing your momentum.
The skier is not a rigid body. There is upper and lower body separation. Just like upper body can be rotating one way and lower body the other with net angular momentum of the whole body being zero, You can have your legs moving faster than your upper body or slower than your upper body. How much faster than your belly your legs are moving does not affect how much total momentum you carry at your CoM, but it does effect how much effort you have to put into slowing your momentum at the time of impulse of the skis with the mogul face.
A little thought experiment for you. You are skiing with a heavy (how much do you think your legs weigh), but bouncy medicine ball. You throw it at the mogul. This speeds up the ball and and slows you down. The total momentum of you and the ball together does not change. The ball hits the mogul and bounces up, loosing some momentum and continues forward at a reduced rate of speed because it struck the mogul at an angle. You did not have to make any effort for the ball to loose momentum when it hit the mogul. You then catch the ball and throw it at the next mogul, and repeat.
When you push your legs forward, you exert effort, like throwing the ball. When you let them absorb the bump all by themselves without resiting at all, it's like the ball hitting the mogul.