Even plaintext can be secure with the right other measures. Air gapped in a physically secured, access controlled location, with all egress/exit points covered by sufficiently rigorous security measures? You're fine.

Encryption introduces it's own SPOF's. If you'very never had a power failure in the middle of a key rotation, you've never been bitten back by your attempt at securing everything with cryptography. Or worse, corrupted by sketchy hardware.

Defense in depth, and proper threat modeling is key. There is also the very real question of "Do you really need that Internet connected anyway?"