I just read it, and you are completely extrapolating what that paper says. It does not say steganography is hopeless. It contains no mathematical proofs, and it's also from over 15 years ago.
More generally, "we do not have a proof" does not mean "we disprove". You also completely ignored my point about the secret, without which the encoder will not work when an attacker tries to run it.
More generally, "we do not have a proof" does not mean "we disprove". You also completely ignored my point about the secret, without which the encoder will not work when an attacker tries to run it.