Yes, hash functions only approximate one way functions since we haven't technically created one - your point here is what I was referring to by mentioning the random oracle model.
But the random oracle model is fully theoretically sound - I'm not sure where you got the impression it isn't. Do you think everything outside the standard model of cryptography isn't theoretically sound? What, then, is your definition of soundness?
ROM is not sound because there are constructions that are provably secure that cannot be securely instantiated. I do not deny that it is pragmatic or that the problems have not been relevant in practice, but the ROM is just a heuristic.
