This post comes from a person that is a fan of Kakuzu (
but I am in no way a fanboy) so take what I say with a grain of salt, but don't dismiss it either
So lets get to the point. "do I think that Kakuzu's earth spear is overrated" ?
and my answer would be, no I really don't, infact I think most people still underrate it...
People just don't grasp how good of a defensive tecnique it really is, or to be more correct: How though diamond actually is.
To be able to penetrade/brake Kakuzu's earth spear you will have to have a high level lightning ability, or a weapon made out of diamond and or at the very least a diamond tipped weapon (
arrow, blade, what ever)
does this means that Kakuzu us invincible ? well Tecniqually yes, as long as Kakuzu have his Earth Spear covering his whole body, and his opponent does not have a diamond weapon or a high level ligntning tecnique, he can't be hurt.
But you also have to realize that there is a reason why Kakuzu does not go around with his Earth Spear always acticated and covering his whole body.
Earth Spear takes a constant amount of chakra to use when activated, and it must clearly be so cost efficient that he can't walk around with it all the time (
else he would always be doing it right? why only be immune to all damage some of the time? if he could be it all of the time without a drawback right?) but on the other hand it can't be to chakra expensive either, else he would be more prone to dodge attacks, instead of just choosing to tank them "with earth spear" So it appear to be a tecnique he can active more than just a couple of times, but not a tecnique he would want to stay active, especially not if it coveres the whole body. (
the more of the body affected by the Jutsu the more chakra is needed to keep it active? atleast that is what I expect)
So Kakuzu's speed must be severily impacted by this Jutsu if it coveres his intire body, it should either render him unable to move, or at the very least make him so slow that almost any ninja would be able to run away from him.
And don't forget that the Earth spear is not instant, it's fast yes, but it does not cover his holy body instantly (
which means that Minato could use FTG to stab him for example) So if you can get the jump on Kakuzu he will not be able to activate it.
So now the question comes if Kakuzu can tank Tsunades Punch with full power without taking any damage (
both external and internal) and here I would say, Yes he should be able to do that, Diamond is just that unbreakable. Tsunade have simply not shown any feats that proves that she could make a Punch (
or a kick for that matter) that was strong enough to shatter diamond. (
if you slammed a sledge hammer down un to a diamond it would be the sledge hammer getting a dent in the Iron, and not the diamond taking damage)
and then we comes to Futon Razen Shurikan, can Kakuzu's earth spear tank it? and yet again my answer would be: yes Kakuzu's can tank it (
and before you go screaming FANBOY over and over, hear me out first!)
what is Naruto's Futon Razen Shuriken essentially? "It's litterly millions of very tiny wind enchanted needle's" (
that is what it is, nothing more and nothing less) and as long as Kakuzu have his Earth Spear activated, and if it coveres 100% of his body, He should be able to tank it without taking any damage what so ever. it dosen't matter that the "needel's are very, very small, or enchanted with the Wind element they can't penetrade his diamond skin. (
had they been based on Electicity, Kakuzu would have been done for, the earth spear would have done nothing then)
So to sum it up: As long as Kakuzu see the attack comming he should be able to tank anything that is not a Lightning tecnique, or some sort of diamond based weapon.