It was a well planned trick.. Itachi was SEverly limited in abilities.. Kakashi AND Naruto worked hard to take out Itachi
i think you got things wrong.
Only the chakra and stamina of itachi was limited to 30 %
and kakashi+naruto defeated him in a short time
naruto wasn't needed, the original of kakashi also could have land the final blow, but kishi wanted to show narutos new rasengan.
Kakashis counters to itachis fighting style are doton hiding like amole + clone feints (fooling genjutsu), multiple clones (avoiding amaterasu by making it a waste of much chakra), mud walls to block the line of sight,suitons for the itachis katons, opening the 1 gate to keep up with the sharingan, dog summons to increase the numbers and attacking from all sides, beast runners against itachis clones,
raiden to cut susanno or hiding like a mole to outlast him.