Doesn't 1:1 correspondence between input and output just mean the compiler output is deterministic. There is no requirement that the output is machine code. For example cfront [1] was a complier whose output was C.

To me that points to the real the step change in LLMs. They are not deterministic and they always give a result to any query. Even if the query is invalid, missing data, or has no possible logically correct answer, you still get a result.

[1] https://en.wikipedia.org/wiki/Cfront