So far in my experience the big difference between the I guess transmission chain of the old flatfooted walking and the new arched-foot stuff is that in the flatfooted system:

the feet are in full contact with the ground as a base, from which force is transmitted to the pelvis, with the calves and quads flexing to stabilize. Almost all motive force is generated by the quads. Stability is then transmitted from the sacrum up the spine to the upper body and skull. Twisting of the shoulders and upper thoracic spine is key to further articulation.

And with arched feet:

The pads of the feet are in firm contact, but the rest of the foot is kept sprung to some degree. The muscles around the ankle largely stabilize the transmission through the knees to the pelvis. The fold at the waist is much more live, powered by muscles at the groin and lower back.

Stability feels to be transferred to the spine not through the sacrum but from the iliac crests to the lumbar vertebrae some distance off the pelvis. Torso twisting is usually handled in the lower thoracic spine. With motive force being added at many points in the chain, I am more efficient and can carry more weight before being encumbered or accumulating fatigue.