This is also the kind of thinking that people use for public-key cryptography: it's perfectly possible to guess the private key of any TLS cert, for example, it just takes a very long time with today's computers. Future computers may well guess it very quickly, so should we stop using it?

Cryptography is a moving a target. Any cryptographic method except an OTP used with perfect opsec is brute forceable, and will need to be changed when your threat model changes (for example, when computing speed advances significantly).