Kage-bushins have a BIG PROBLEM!
It divides the user chakra, any normal ninja would 'gimp' himself using a Kagebushin for anything other then spying.
Naruto can counter this weakness because he is a botomless pit of chakra.
So he is the only that can efectively use bushins to the full extent, he can efectively create a clone of himself, same amount of chakra, same skills etc..
You saying that no one should ever be credible for solving a puzzle, because you get all the pieces and a picture on the box..Plus i don't have a problem with kakashi teachin' him, i have a problem with kishimoto saying that he would come up with on his own only to be helped by kakashi later.
Kakashi only told him, the one with straight lines are the corner pieces
Now putting all togueter was naruto's work..
He wasn't spoon feed with sharingan copying.