Understood, but also understand that Grouchy was not popular among Bonapartists, and indeed was the cause of the defeat, don't you know:
From an 1869 grammar book:
Les alliés auraient été vaincu à Waterloo, sans un malentendu du général Grouchy.
They didn't mind taking away his Marshal's baton!
Why did it take until 1831 for d'Erlon? What made Grouchy special?