Lets not be ignorant. True, both were capable of wielding the Kubikiribocho with ease, however, Zabuza has a 4/5 for strength in the data book and Kakashi has a 3.5/5 in the databook for strength even in Part 2. Zabuza is physically stronger than him thus he can wield it faster, even if it's slightly.lets not push it.Both were capable of wielding zabuza's sword with one hand like it was nothing.
This is off topic though so who cares