About the paper: if someone has gotten access to your identity (private) key, you are compromised, either with their attack (adding a linked device) or just getting MitM'ed and all messages decrypted. The attacker won.
The attack presented by Google is just classical phishing. In this case, if linked devices are disabled or don't exist, sure, you're safe. But if the underlying attack has a different premise (for example, "You need to update to this Signal apk here"), it could still work.
The attack presented by Google is just classical phishing. In this case, if linked devices are disabled or don't exist, sure, you're safe. But if the underlying attack has a different premise (for example, "You need to update to this Signal apk here"), it could still work.