Information-theoretically secure encryption and authentication do exist, so in a sense unbreakable (authenticated) encryption is a fact. Outside of that, the existence of OWFs is indeed an assumption, but I doubt anyone's losing sleep over it.

The original argument didn't make sense to begin with: the SIGABA rotor machines used by the US during WW2 were never known to have been broken during actual use, so the only reasonable conclusion about cryptography to draw at the time was that Enigma was simply a poor instance of it.