samaheda has shown to be able to absorb big amounts of chakra in little time.. as it was able to absorb
four tails of the hachibi with one swing. Kisame also has his great shark bullet wich absorb other
chakra based jutsus. hes shown to be able to change the battlefield with one jutsu.
kakuzu is an experienced ninja who fought againts even hashirama and survived.
he has the advantage of being able to separate his body into element creatures wich would put
kisame and kakuzu in a number advantage.
I know you already agreed to some points, but I thought I'd answer these anyway...
Like I said, samehada can absorb as much chakra as it wants, but jinton instantaneously engulfs. Even if samehada was already in absorb mode it can't protect all of Kisame, not his back, and certainly not Kakuzu as well. And Kisame doesn't know where Muu is so he can't use the shark bomb; even if he did Muu would just fly and jinton from a different angle. That's another point for samehada-- if Muu jintonned Kisame's back it would take him out even if samehada absorbed in time to save itself. Changing the battlefield and experience don't matter because Muu flies and they can't sense him. And lastly, "numbers don't matter to a jinton user like me." Muu can dust the entire battlefield, Kisame, Kakuzu, beasts, and all, in an instant. Like I said, he's mad haxxed.