The issue is that all cryptography depends on one-way functions, so any ability to break a cryptographic algorithm that depends on one-way functions in a scalable way means you have defeated almost all of cryptography in practice.
So in one sense, a mathematical advance on a one-way function underlying a symmetric key algorithm would be disastrous for overall cryptographic prospects.
The issue is that all cryptography depends on one-way functions, so any ability to break a cryptographic algorithm that depends on one-way functions in a scalable way means you have defeated almost all of cryptography in practice.
So in one sense, a mathematical advance on a one-way function underlying a symmetric key algorithm would be disastrous for overall cryptographic prospects.