It is generally regarded that 70%-odd of the "hit" is in the tip, and another 25%-odd of the hit is in the first 10 inches of the shaft. That leaves only 5% of the hit to be found in some combination of the {rest of the shaft, joint, butt, rubber bumper}.
Thus, the joint is more about controling the weight and balance point of the cue than having anything to do with how the cue delivers energy to the CB.
Thus, the joint is more about controling the weight and balance point of the cue than having anything to do with how the cue delivers energy to the CB.