A signature is good in this use case: 1) You have a public key you trust. 2) You get a message + hash + signature. You want to verify. What we had here is:

A signature is good in this use case: 1) You have a public key you trust. 2) You get a message + hash + signature. You want to verify. What we had here is: 1) There is a DNS record with a signature value only. 2) You send the public key + the message, and want to get the same signature value. This isn't secure, as per the article.