The technology of the Prussian, Austrian, and Russian systems were all three older than Gribeauvals. The Prussian designs dated from the 1740s, the Austrian from the early 1750s, and the Russian were copies of the Austrian models. The elevating system, the screw quoin was developed by von Holtzman in the 1740s and copied by the Austrians and Russians. The gun carriages were all of the older type, which absorbed recoil only to the rear and not of Gribeauval's new design which were designed to absorb the shock of recoil both to the rear and downward. The French ammunition caisson was water proof.
Some other innovations:
-the screw vent
-adjustable rear tangent sight
-a newer, more accurate and efficient elevating mechanism
-windage improvements for greater range and accuracy.
-better tooling for the testing of rounds regarding windage
-brass wheel housings for better and easier maneuverability-this was a mechanical advantage which assisted the gun crew
-better designed and constructed gun tubes in the 'three calibers' which were definitely superior to the Prussian and Austrian models, as well as being more robust with a longer service life.
There is no evidence that the French 8-pounder was too heavy. That's been stated too many times and with no documentation. The French artillery arm certainly didn't think so. You're neglecting the different weights used by the European powers. A French pound did not equal an English pound did not equal the Prussian or Austrian pound. The French 4-pounder was over four English pounds and a French 8-pounder was almost nine English pounds. The Austrian pieces had rounds that were less for each-the 3-pounder was less than three pounds, the 6-pounder less than six English pounds, etc. The later AN XI 6-pounder had more throw weight that the Austrian 6-pounder. Using captured ammunition was certainly possible, but it wasn't without inherent problems of windage which would affect range and accuracy.
I do not agree with your assessment that Gribeauval's technology was Seven Year's War vintage. There was too much new material, tooling, and practices that came with the new system. The Prussian and Austrian systems were pre-Seven Year's War, and technologically the Russian system was behind that of the French.