Certainly an interesting statement from one who beleives that Prussian artillery was so poor. I think you have forgotten the influence of the Berlin Academy of Sciences, Euler, Scharnhorst, Desckau, Muller, and many others. Ah yes they were not French. So we use Napoleon's counting method.
The Prussians created and proposed that were taken up by other countries including France.
1. Horse artillery (1759),
2. Reduced charges so lighter guns (1740s),
3. Chambered guns as a precursor to the Russian Unicorn and Saxon Shell gun (1740s)
4. Developed the howitzer as a field piece (1750s)
5. Ammunition limber (1750s)
6. The lighter guns permitted them to be conveyed with the use of ropes and poles (1720s)
7. The creation of an artillery train with horses already specified under the Canton System (1730s).
8. Mobile regimental artillery and tactics learned off their Swedish allies [Gustav Adolphus]
It will be accepted that the Prussians did not adopt the horizontal boring system until 1805 and the next year the French took it for reparations. Production of the new pieces of artillery based upon the best methods and designs in Europe from the work of Scharnhorst were slowly produced from 1809 and were not codified until 1816.
The predudice towards artillery was more of the cost of it. Frederick during the 7YW lost three complete systems of artillery. The M1768 system was lighter than the Gribeauval System at 141:1 compared to 161:1 yet being the same length in calibres. The Gribeauval System was a reaction to the Seven Years War and was not as developed as those countries who had active participation in the AWI where mobility was king. I would refer you to the Hessen Kassel, Hanoverian and British developments. There were like the French two weights of pieces for different uses, the light pieces for field operation and the other for position / garrison work. Alas this seems to have been missed by a number of authors.
"The Prussians learned their artillery lessons from the Napoleonic period and their artillery arm became excellent in both skill and equipment before the next European go-round when Prussia launched on the Wars of Unification."
Yes and much of this came from hiring the best in artillerymen and thinkers in Europe. A good start was a Hanoverian who you might recognise. His treatise upon artillery was translated even into French in the 1830s.
"What is definite is that by the time the canister round left the gun tube, the individual balls were free of the canister. That can be proven by the gunnery tests when canister was fired at a fixed target."
No it is not and I will take you back down the art of experimental design. The experiments showed the effect and not the flight of the cannister or the balls contained. As far as I am aware that there were no targets at the muzzle or within 100 feet so it is unclear as to what occurred. All we know is the number of hits at 100+ yards. There is a problem in putting a target too close to the muzzle would be the muzzle flash that would be over 60-70 foot long and the expansion of gases from the gun tube punching a hole through the target. Remember that gunpowder is NOT an explosive, it is a propellant relying upon the huge expansion of gas [1 mole = 22.4 litres of air or about 50g of gunpowder - rough approximation as it assumes complete combustion.]
"Tin isn't the strongest of metals"
It is a ductile metal and will expand especially when heated.
"The act of firing the piece with an adequate charge would be enough to rupture the canister and get the desired effect of the round."
Now what I have been talking about has been how this spliting of the cannister occurs. This is unclear to me and any of the writing whether contemporary or not, the manner of this and the process rather than the effect.