When was it mentioned that a nin can distribute the amount of chakra to his kagebunshins at will? Didn't the 3rd hokage say that the reason he does not make more clones is because it will equally distribute his chakra to all of them and is too risky? If he can just put a drop of chakra in each clone (like you are saying naruto is doing) then he could have made dozens of clones in his fight with Oro.

I think this is also the reason other nins don't use kagebunshin all that much. Unlimited chakra is indeed Naruto's redeeming point.

Also, I think all Kagebunshins, no matter who makes them, disappears after one hit.