Certainly, but your proposed scheme does not feed entropy back into the stream cipher, it just offsets its output. Which effectively introduces entropy into th

Certainly, but your proposed scheme does not feed entropy back into the stream cipher, it just offsets its output. Which effectively introduces entropy into the output, as well as to the internal state of the stream cipher. This can be trivially broken if the stream cipher key ever leaks. This is a trivial restatement of how symmetric ciphers are supposed to work.