You keep evading the question posed by Digby which is how many different sizes of wheels were part of the Gribeauval system?
If there were as many as 20 different sizes of wheels, I would submit to you that this system was not as good as you seem to believe it was.
Having read over many of the posts on the subject of respective French artillery systems, and knowing a little bit about the Gribeauval system myself, I am starting to come around to the view expressed recently on this forum that the Gribeauval system was basically a response to the problems evident in the French artillery which were exposed during the Seven Years' War. In essence, it was designed for the previous conflict and not the conflict that France found itself in, after 1792.
Since Napoleon was an artillery officer and very knowledgeable about the subject, the fact that the French decided to change to the AN XI system indicates to me that he and senior artillery officers knew that that were defects with the Gribeauval system and wished to remedy them.
Why they did not do so, I believe is a simple question to answer -- lack of money. I have referred to this perennial French problem before. France was perpetually broke throughout most of the latter half of the 18thc century and, despite all Napoleon's currency reforms, his plundering of the treasuries of other nations and his imposition of financial penalties on defeated opponents -- not to mention his half-baked economic theories -- he never had enough money to pay for the costs of his military ambitions.
Not to say that the British treasury was in much better shape, although it was, but Britain had a tremendous advantage over France and that was that it had a better credit rating. Bankers were more willing to lend money to Britain than they were to France and even if they did lend money to Napoleon, the interest rates were hellacious. Frankly, the man was a bad credit risk.
It impacts all down the line. No money, no new weapons.