I'd voice the same points made below that heavy cavalry's use as a "shock weapon" was fairly old by 1800. I think the first to employ in this manner was the young Swede Aldolphus Gustavus. Prior to his use, cavalry did not "drive home" in a charge but would wheel at the last moment and discharge a single round from their weapons. He also introduce light mobile artillery to break up the phalanx of pikemen to make them more susceptible to his cavalry charges.
More effective use of bayonettes, better firearms and the square formation eclipsed the use of heavy cavalry by the end of Frederick the Great's era of warfare. An example of this is the poor performance of the Prussian heavy cavalry at Auerstadt.
To me the question would be who or how did Napoleon's armies revitalize the use of this shock weapon? Was it simple a useful tool against poorly train conscripts? Certainly the French heavy's had a hard time against disciplined troops (as at Waterloo) by 1815.