This is incongruous with your original argument: AES is optional, so anybody doing cold storage with PGP on messages they don’t fully control (again, the backwards compatibility story) is going to end up using 3DES.
And no, you can’t brush aside 3DES being insecure for large messages and then call it secure. Modern cryptographic tools don’t allow that, because there is (again) universal consensus that it’s insecure.