That's a massive assumption though.
1. What about charging chakra implies that he was going to use an elemental attack?
2. What about charging chakra implies it was going to be a stronger elemental attack than his other attacks?
Kabuto also used chakra to protect himself against Naruto's rasengan.
All i'm saying is that there's no purpose in trying to decode what Yamato meant. It doesn't even matter.
-What else would it be? He had already changed forms so its not like that was what caused the chakra to spike.
-He showed no charging of that leangth for any of his previous attacks....
It is an assumption.....
You said Atsugai and Hiruzen's raiton are equal, so if Hiruzen used 4 clones and they all used raiton, that shouldn't be countered by Atsugai.
They are not equal obviously as the fuuton is stronger, and I don't think he could really fire 4 massive raitons at one small target..... however Kakuzu's fuuton is really large man, been a while but if all the areas of his fuuton are just as strong striking different spots shouldn't mean that the others can't be stopped with fuuton either. Even if so, it would halt them at the very least allowing Kakuzu to move away, meanwhile he has three other hearts able to attack Hiruzens main body.
Also don't forget Kakuzu can create multiple bolts of his gian, and while he's only shown to fire two that should be enough.
Atsugai> Two raiton
Gian> Whatever raiton break through (if any)
Unless you're going to argue that the raiton has more potency than raikiri.