You know the Sasori puppet isn't featless, right? It actually has some pretty good feats.
Zabuza is facing a very tactically inclined opponent, who was even chosen to lead the Surprise Attack Division for the SA. When the mist goes up, Kankuro can safely take shelter
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. From there, he bombards the outside with poison [
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]-[
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], which should go unnoticeable to Zabuza. Also, Kankuro was entrusted the Mother and Father puppets, so he should have access to them in battle. They can use their
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and stretch it over a long distance at an attempt to blindly take out Zabuza [
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], which is another tactic he can't trace.
Then there are other methods that I can think of to employ that wouldn't allow Zabuza to touch Kankuro before he falls into a trap, that will finish him. All in all, Kankuro is too tactically versatile for Zabuza, and won't lose this fight.