The Prussian heavy cavalry's efficiency had fallen off somewhat since 1763 and they certainly did not have a cavalry commander of Seydlitz' ability in 1806.
French heavy cavalry certainly did better than 'very well' in 1805, 1806, 1807, and 1809. At Borodina in 1812 heavy cavalry (Saxon and Polish) took the Great Redoubt with infantry support. Eylau was one of the best examples of the use of heavy cavalry and dragoons in the period, and I wouldn't say they were up against 'conscripts.'
There are myriad other examples during the period of successful cavalry charges (Somosierra and Montmirail not being the least of them) and I don't think the arm was quite in its death throes yet.
Austrian cavalry had problems not because of the quality, which was excellent, but because of no tradition of acting in mass.
French cavalry before the Revolution was not distinguished and their heavy cavalry wasn't held in too high a regard until the Napoleonic reforms during the Consulate and the introduction of the new cuirassier arm.
As late as 1864 in the Shenandoah Valley, massed Union cavalry was attacking and overrunning veteran Confederate infantry.
For our period, looking at Grouchy's expert handling of his cavalry on the left flank at Friedland is an excellent case study. Another in Montbrun in 1809.