In theory, your professor was right. In practice, not so much. The thing is theory requires perfect proofs. Practice only "good enough" ones. (We will ignore that the one-time-pad is mathematically proven secure, because it has little practical relevance...)
So that state of things is that ElGamal has a security proof relying on an unproven assumption that is very likely true. RSA is much weaker on the theory side and current block ciphers or crypto-hashes are even weaker on the proof side.
As to QC, the problem is that effort seems to scale exponentially with qbit numbers and (!) computation length. That means there are not very large sizes of computations they will never scale to. And, for example, doing RSA 40960 (i.e. 10x larger than the larges typically used today) is not that much of a problem. The second problem is that there is no quantum computation in existence that actually conclusively proofs it even works. The theory may well turn out to be a tiny bit inexact and then everything fails. And "quantum insecure" does not matter one bit if the machine for it cannot be built.
As to QC algorithms, block ciphers are safe, hash functions are safe, some other things may be as well. The reason is the compute mechanism cannot really break them (half bit length for block-ciphers, for example, still completely infeasible to attack if that is 100 bits remaining or so).