Re: has anyone noticed yet?
But still, chakra control can't be seen, it's abstract not concrete. Chakra control is the amount of chakra a person can limit and regulate with their own abilities. Like I said earlier, Rasengan is form manipulation taken to the highest level, there is some form of chakra control used, but it's not 100%.
But still the whole thing is not chakra control, yes it's required, but its minimum. Nature manipulation is the ability to alter the chakra's nature if one is predispossed to it. If it is nothing but chakra control, don't you think Sakura would already be predispossed to any nature of chakra? I think not because her chakra control is probably one of the highest in Konoha.
I think the 4th and Jiriaya had just as much possibly more chakra than Naruto. Although they probably don't have enough stamina to hold the jutsu in place, so they don't have the endurance that Naruto has. Naruto has above average chakra and super stamina, so when he does jutus that require emense chakra, he runs out for a little while, but since he has so much stamina, he can convert that into more chakra.
But if Naruto trained with all of those shadow clones day and night, don't you think he could have picked up something? He probably gained enough experince to use the Fuuton Rasengan without shadow clones. But we will see this coming up chapter or the next.