Having a very simple API is not at odds with security, though. A simple API could automatically seed from the OS and then run a tiny loop with sha2 or sha3, for example.
SHA2 is not designed to be used as a RNG. SHA3 might be a little bit better with its "streaming" modes, but there are many far better and faster ways to get random bits.
2. You definitely don't want your std to be designed with a simple API to a fast, secure, and popular crypto primitive? Pretend I named your favorite one, to avoid bikeshedding issues.