OK let me tell you why Sasori will defeat current Kankuro with easy difficulty.
Sasori and Kankuro fought each other before and we saw the difference between their puppet mastery, Sasori defeated Kankuro with no difficulty and nearly killed him, he held back and didn't kill him in that fight because he was certain his poison would kill him, and it indeed would've killed him had Sakura not created a special antidote for it.
he was just too much for Kankuro plus he knows the weaknesses of his puppets and how they work, because he was the original creator of them.
Now let's see what happened in the war, when Sasori fought Kankuro, he didn't have his 3rd Kazekage puppet, nor did he have all of his other puppets, in the other hand Kankuro had all his puppets plus Sasori's body, so Sasori was clearly at a disadvantage there.
But even though he was at a disadvantage, he could've defeated Kankuro if he was serious, remember Sasori's puppet mastery > Kankuro, that's what made him an S-Ranked ninja and that's what made Akatsuki accept him as a member.
Besides, Sasori has a genius level intelligence, Kankuro was never stated to be a genius or even close to be a genius.
Sasori's puppet mastery compliment from Kishi directly:
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Sasori is called a genius by Kishi himself:
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