Comment by colmmacc

Here's we're talking about hybrid key-agreement. It's more like you agree secret A with a peer using the magic of Diffie-Helman, separately you make up secret B and encapsulate (which is basically a form of asymmetric encryption) that using a PQ algorithm and then send that on, and then derive C by mixing A and B. You're not actually encrypting something twice.

Some government and military standards do call for multiple layers of encryption when handling data, but it's just that multiple layers. You can't ever really make that kind of encryption weaker by adding a new "outer" layer. But you can make encryption weaker if you add a new "inner" layer that handles the plaintext. Side-channels in that inner layer can persist even through multiple layers of encryption.