There isn't really such a thing as a "precise written" language.

I don't know. I think written languages are inherently more precise by virtue of expansion beyond individual comprehension. Nuance can be preserved. I could be wrong, but the morphology and lack of historical material to study in oral languages make it hard to say one way or the other. It seems like oral languages have been expanded by proximity to European concepts through colonization, often using bastardized alterations of English words, though.

Language does affect the way we think and the way we think affects language.

I'd say further, the way we think affects our cultures, and the cultures we create affect the selection pressure of favored genetics, reciprocating back into the culture. Language seems more a reflection than a cause.