That requires a MITM. A typical cybercriminal isn't in a position to MITM me. But every cybercriminal on the internet is in a position to steal my bitcoins (if they can break bitcoin crypto).
If you have a mossad problem, big integers were never going to save you from that before or indeed, after QC.
OTOH the typical cybercriminal wouldn't have access to quantum computers for a while so this is a pretty unscary prospect either way, for now.