What is "important" for a ninja, I believe, is by default their best growth stat.
mei thou, while very dependent on nin for most of her abilities, is made intentionally weak on nin growth to counter her awesomeness elsewhere(see the *beep* thread complaining about the fact that she have 4 debuffs and claiming that she have no shortcoming in anyway to balance against that)

So you end up with a ninja that should be relying on nin, but is told that tai is her "good stat"