sorry i don't understand what you are talking about, flying on top of the iron sand is fanfiction and please don't post the scan where chiyo says that sasori can change the shape of the iron sand like he wishes again, because that doesn't prove that he can create a platform where sasori can fly on.
That belongs not to his feats and is just a assumption !
And even if, do you think kakashi would just led sasori prepare a iron sand platform or sty like that without interfering ?
Sasori start in hirkuo and this is actually his death sentence due to being slow as shit, Kakashi blitzes with raiden which would cut through hirukos tail together with sasori inside the inactive puppet.
okay now we are supposing that sasori is able to get out of hiruko in time, he has to summon the 3 kazekage with a scroll, which is enough time for kakashi to blitz him via 6 gate speed + lightning blade.
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Now lets supposing sasori would summon the 3 kazekage also in time, he has to use hand seals to activate the iron sand
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again it is enough time for kakashi to blitz with a jutsu which doesn't require hand seals, Raikiri or beast runner blitz.
The 3 kaze kage is a offensive puppet who never shown a defensive jutsu like shielding itself from all sides.
Kakashi still can reach the puppet from underground or Kakshi vanishes with hiding like amole and appears behind the puppet between sasori and the kazekage while cutting the strings with raikiri to make the puppet useless, now kakashi can decide whether he blitzes sasori in front of him along with his heart (sharingan can see the color of chakra when nothing is blocking its line of sight) or kakashi turns around and destroyes the 3 kazekage with raikiri.
I don't know why you are still denying kakashis ways of bringing down sasori, in my opinion you completely are ignoring Kakshis speed feats and his other skill areas.