To undestand the Zekes construction n philosophy we can look at the Iconic Japanese warrior, the Samurai. His offensie weapon (sword) is also his defensive weapon. No 30kg metallic shield there.
The Zero was designed to have extreme agility, lethal guns, fantastic maoeverability and long range. All offensive traits that when used correctly can also be good defence. Suppose its the ultimate example of "attack is the best defence".
Im a P38 nut, so usually Zekes are my targets, but a well flown A6M2 can offer a better challenge than a poorly flown SpitV. You just gotta love it for that. Like so many other planes, the plane only amplifies what the pilot's all about.
Besides, how many other planes were capable of ever being launched off a Submarine???