The champions do back off and charge, though. And they always seem to rush the same target at the beginning of the fight, which almost instakills your mount after a few seconds. They also refresh their shields constantly. Maybe I'm doing something wrong, but I can't even seem to dent these guys. Sitting back against a wall and not using charge doesn't do anywhere near enough damage and there aren't enough mounts to refresh your ride as fast as they can damage you.