2. what? Zoro is not a normal man he is a skilled swordsman trained by a Warlord. Also he is stronger than most of the people in the in Naruto.
You are highly underestimating the effect of numbers. Then again, that's par for the course in the anime world.
Consider this: Guns superceded arrows on the battlefield, even though they were, at the time, far less dangerous than arrows on an individual level. Why? Because you could put a whole lot more of them on the field.
Skill and ability is important, but it isn't everything. I think it's naive to think that even most superhuman characters can take out entire armies, unless they are on the level of absurd destrctiveness similar to that of DBZ, where characters can toss around WMD level attacks like toys.
Also, Naruto ninja use traps and ambushes pretty regularly, and even for the flashy loudmouth ninja like Naruto , misdirection is the key element of their attack strategy.