You are very wrong. Address reuse is advised for privacy so far quantum computers are not yet a threat. It is quantum computers that will later let it be of security concern.
Not quite perse.
Here you can see where there was a flaw in random number generator for ECDSA and some addresses were affected
https://bitcointalk.org/index.php?topic=581411.0If the address wasn't reused or remained unspent, then the movement of their funds wouldn't had been possible.
Unspent address protected by SHA256 and RIPEMD160(which hide their public key) and ECDSA (which secures the private key)
Reused address( the one after spending) have their public key exposed so their security relies solely on ECDSA which is susceptible to future quantum attack
and vulnerability in ecdsa generation. I believe we talking about P2pkH.