Evidently you think the critical hit rate boost is just an attacking trait but no, is also a defensive one.

Lets consider a 30k critical hit kushina vs a 30k critical hit kakuzu.

Kushina stacks with the passive +2 6% nin and 6% crit rate per endured hit.

What does this mean?

That once she was hit 6 times by the kakuzu team (basically start of round 3 in the worst case) she gets a 36% boost to her critical hit rate and how high her critical rate becomes?

40800.

So what happens since this moment onwards?

That the enemy kakuzu ceases more or less to crit on her while every single hit she will land on kakuzu will be a critical hit and moreover every mystery and standard attack she will suffer will increase her ninjutsu by a further 6%.

So are you really sure kakuzu will win on later rounds considering she selfheals by 20% of her basic ninjutsu for every standard attack and mystery she uses (passive +2) while kakuzu just selfheals once and by a way lower amount?