So you're right that this is a bit arbitrary because the line between the standard lib and the language is blurry, but someone writing Rust is going to expect Vec to work, it doesn't even require an extra "use" to get it.

Perhaps a better core example would be operator overloading (or really any place using traits). When looking at "a + b" in Rust you have to be aware that, depending on the types involved, that could mean anything.

Anyway, I love Rust, it just doesn't have the 1:1 relationship with the assembly output that C basically still has.