never heard anyone saying pelvis is part of the upper body in any kind of anatomy. that's absurd. focusing on pelvis has nothing to do with the how much u use the 'kinetic' chain. the spinal chord and the pelvis is the main control point of all parts of the legs and feet. to move and place the feet at the right position so they can push up the ground the hip controls that. right positioning of the hip in regard to the feet and its angles in 3D is the main contributor of overall balance of the whole body and frequently referred core usage. simple force transmission from feet after they are touching the ground and controlling the feet from the hip are two different things. different viewpoints and both valid in different context.