"A puppet master's ability is measured by the number of puppets they can wield."
That is what was said in the manga. For 'normal' humans the most puppets possible is 10. Chiyo can use ten at once. What's the max puppets Kankuro has been seen using? Four or five? Beyond that the quality of Chiyo's puppets are beyond all of Kankuro's except for the puppet of Sasori. Ten great puppets beat one great puppet + four decent puppets.