I think it depends. Imagine a future where quantum computers may be in reach by intelligence agencies, but a quantum-resistant public key encryption algorithm h

I think it depends. Imagine a future where quantum computers may be in reach by intelligence agencies, but a quantum-resistant public key encryption algorithm has been proposed but not rigorously defended. You wouldn't want to trust either algorithm alone, so you can use both: encrypt the data with the quantum algorithm first, then by the classical one. Decrypting would require breaking both, there's no shortcuts.