It’s both, actually.
The quantum computing concern has more to do with the ability to derive a private key from a public key and move coins.
While it could also have impacts on mining, the primary concern is that of security of value stored on-chain.
nostr:nprofile1qqsqqqqqqqpn93urrkw94x03swhu9qf6da56zmka5lm0crkczyzkdespr3mhxue69uhhyetvv9ujummjv9hxwefdvde82umg9e3k7mgpr9mhxue69uhkzer4d36zuvfcwpk82uewwdhkx6tpdsq32amnwvaz7tmjv4kxz7fwd4hhxarj9ec82cs9c3ady, bully me if I'm wrong here. 💜
Discussion
Yes, you are both right; but Grover's is much harder to run than Shor's, so signatures are the most vulnerable, then 160-bit hashes. 256-bit hashes are very very hard, and might require a truly enormous computer to be competitive with ASICs. But once those achieve advantage, miners will just upgrade and in 2 weeks or so things will be alright again.