Before and at impact, the head is moving based on it’s own mass and dimensional characteristics. It is free wheeling through the impact zone. Therefore the mass that we call a golf club head, at it’s static data as you called it, does determine how the head moves. Cochran and Stobbs first touch on this way back in “The Search for the Perfect Swing” and Ralph described it in his original Golf Club Fitting, Design and Repair book. Once the shaft releases (head goes from lag to lead position before impact) the head is operating on it’s own mass and dimensional characteristics. The shafts sole job is to deliver the club head to the impact zone as consistently as possible. Swing mechanics put the club head in motion, or orbit around the body, and hopefully with good technique, sets the shaft to be in the best position to deliver the head in the best way possible. But understand, once that shaft releases, it’s the heads mass and dimensional characteristics (along with it’s specifications, like loft and lie angle) that have the major influence on the strike and the ball flight.