Chie, yes I used a plural, because 99% of the time, people only pick on people's grammar/spelling when they are losing the argument.......and on that point you were wrong as well. "Defense" and "Defence" are practically the same word-it's just that defense is the American variant, whereas British/Australia tend to use defence more.
Second of all, the point is, kamui BLOCKED kamui(as it can be used for both attack and defence). The yata mirror cannot BLOCK the yata mirror, as they are both shields. I can't believe I have to explain it.......
Nice to know.

Sorry if I came off as a jerk before. I wasn't really being all that serious though about the grammar, you can spell words anyway you want to. I just wanted to see how you'd react. xD
-What do you think will happen if for instance a Yata Mirror collides with it's equivalent? So you don't think that that they'd be even? I don't think one would break, that's for sure.
To back up my the point, the kabutowari is said in the databook to "break through any defence" So what happens when the yata mirror and kabutowari meet? It would obviously end in a paradox.(similar to the third raikage incident) As I said, using the no limits fallacy with the yata mirror is stupid.
On the Kabutowari point, yes this blade that was used by one of the 7 swordsmen of the mist was said to be able to cut through any defense. However, that's not necessarily a paradox and if it collided with Yata it's not quite discrediting the hype for it. Yata mirror changes its properties to match the attack coming at it, so it would be like the Kabutowari blade going against a Kabutowari blade. It would be neutralized.
And as for the 3rd raikage incident, yes only he himself could damage his defense, but that was his own power. I guess this is up to one's point of view. Even though one's own defense may be there weakness at times, because for certain defenses in this series that's the only thing that can match up to it, I wouldn't exactly say that everything stated in the databook about it is bs due to that...it's kind of normal. When something goes up against it's equivalent, it's going to be matched. Or if someone had a defense made by themselves, when they go against there own offense (like in the case of Kakashi vs Obito's kamui) it'll be matched or if someone goes against their defense with their own power (Raikage's defense only penetrated by himself) it'll lose. That's expected. But if you put the 3rd raikage's defense against anything else (bar things that absorb ninjutsu or neutralize it), then it will be fine...hype not quite discredited here.
However, there is not an attack that can go against Yata, nor will there ever be considering its one user is long gone. But once again, that hardly matters. The shield has lost relevance to the series, it can be bypassed, and the one user couldn't hold it up for a long time. I don't see a weakness with the shield, just the user himself.