Custer stopped JEB Stewart. Stewart was supposed to attack from the rear as Pickett conducted his charge.
People like to trash him since the 1960s. But he pretty much saved the union that day.
Grant literally gave him the table the Appomattox surrender was signed on.
And Pickett was a decent man. That disaster at Gettysburg broke him. He never truly recovered.
Custer was also excellent during the Peninsular campaign.