What additional point did Yehoshua raise here?
Malbim: If You will say that even without Hashgachah, we are stronger than the Kena'anim and we can defeat them naturally 1
Was there such a Havah Amina? Yehoshua and Kalev did not contradict the other Meraglim about the size of the Kena'anim, only about our ability to defeat them with Hashem's help! Perhaps after their hearts melted, we were stronger. (PF)