With all due respect, from an aerospace engineer, your reasoning is flawed. You are only considering muzzle velocity which really doesn't mean a whole lot since we don't shoot turkeys at 1 or 2 yards very often. The smaller shots sizes are significantly superior from an aerodynamic standpoint because they don't have all of that surface area drag to slow them down at such an exponential rate when compared to say a #4 lead. The second advantage to the smaller shot size is based upon the same premise. The smaller surface area significantly reduces drag (think FMJ bullet for comparison) when the shot enters the animal's skin which leads to less velocity bleed off on its way to bone (important because we are trying to break in his neck). The final advantage is how hard/strong the TSS shot is compared to lead. Lead deforms significantly upon impact (with each other going down the barrel as well as hitting something downrange) which hampers its ability to maintain its entry velocity and subsequently reduces the velocity/energy upon contact with bone (think FMJ ammo again).

When people talk about #4 lead being equivalent to #9 TSS, they are talking downrange (i.e. where it matters) and not at the muzzle. You are correct though that the 4th advantage is so many more pellets on target, significantly increasing the chance of breaking the neck at various yardages.