The issue here is that Schneier is discussing brute force forward computation of cryptography (IIRC of AES). Quantum computers don’t iteratively attack primes by attempting to compute all possible primes. The current conventional computer attacks against RSA also aren’t brute force hence why the advised size of an RSA key right now is 4096 bits.
This calculation only holds if there is no faster way than brute force iterating the entire key space.
The issue here is that Schneier is discussing brute force forward computation of cryptography (IIRC of AES). Quantum computers don’t iteratively attack primes by attempting to compute all possible primes. The current conventional computer attacks against RSA also aren’t brute force hence why the advised size of an RSA key right now is 4096 bits.
This calculation only holds if there is no faster way than brute force iterating the entire key space.