Well, because your load is 3 balls seated against each other, I can only assume (as I have no empirical data for proof) that each ball is obturating when shot, thus when now spinning out of the barrel. all three balls have some "flat spot" on them (one ball has 2 flat spots) and the rifling will cause the flight of the ball on each one to be much different.
So, I very much doubt the balls are close together when they hit the target. Thus, you still only have 3 balls hitting the target with roughly 556-ft\lbs ME each, vs one ball at 1,631-ft\lbs ME.
Outdoor Life magazine states that a minimum of 1,000-ft\lbs of energy is needed to ethically kill a whitetail deer. None of those 3 balls from a 3-ball load even approaches the minimum suggested energy levels. The single ball load exceeds the 1,000-ft\lb easily.
A big game animal drops within feet when there is immediate massive stoppage of blood flow to the brain, and\or a severance of the neurological system.
Again, I will trust my 1,631-ft\lbs of energy to do the job vs chancing the penetration depth, and accuracy of any 3-ball load (556-ft\lbs) from a flintlock rifle.
Dave