Because it's been repeated so much I too believed that heavier a/c builds up more speed in a dive and then retains that energy better into a zoom climb vs. lighter aircraft. Running through loads of dive/climb modeling has shown me this is completely misleading.
dtango, I fully agree with your theory, but I am not completely confident in its application to reality. There is a reason why pilots believed the P47 zoomed better than other AC that had better Ps ( though if one goes high enough, the P47 wins in Ps when the other's engine dies of hypoxia...). At the same time they ALL preferred less weight given the option, but this is not strictly with zoom ability in mind. Equal planes were never considered - it was not a P47 vs. a P47 with a ballast stone in it, but a P47 against a P51, or a 109. If the planes have only a small difference in power loading, the kinematic part (weight and drag) play a larger role.
One reason for advantage of heavier aircrafts is that pilots were more worried about the initial part of the zoom. The threat range for gunfire was quite short and gaining a few 10s of feet DURING the zoom could be enough to get them out/in of the threat. Higher mass gives an advantage in the early zoom when starting from high speed. The last part of the zoom is where power loading dominates and where the planes are flopping about, left them too little control to make a shot - I doubt many pilots of high torque planes will be keen on kicking the rudder to align the shot, while on the verge of a stall with the nose pointed straight up.
The second related possible consideration is that we integrate the zoom too long. Most of the advantage of a light plane with (just a little!) better Ps comes in the last stages of the zoom, when it is crawling up close to the stall. We assume that the pilot will keep his noise pointed up, full throttle and fight the plane till its starts falling backward. I seriously believe that most pilots will not go as far as this and terminate the zoom much earlier. Doing a tail slide is one thing, doing a tail slide at full power... that sounds a bit dangerous and likely end up in a spin. We hear many reports of planes that were hard to control at a steep angle, full power climb. It was supposedly one of the defense moves of the P-38 to go into a steep spiral climb to the right so high torque 109/190 will not be able to follow and eventually flip over to the left. I do not know if this is really true, but this is the anecdote.