That said, I should point out that there is nowadays a loophole for special-casing labels that begin with underscore, called out by the SVCB document. The loophole does not allow for dropping the client requests, though.
On the gripping hand, all that this report boils down to is a rediscovery that if the queried server does not answer immediately, there's a window for an attacker with access to the path between client and server (or at least the ability to blindly route packets into that path with forged source addresses) to inject forged responses; that the message ID and random port number system is woefully inadequate for making brute forcing hard at even late 1990s network speeds; and that most of the mitigation techniques for forgery (including the PowerDNS one called out in this report) are useless if the attacker can see the query packet go by in the first place. The right answer is proper cryptography, not nonsense about punctuation characters that are supposedly "malformed".
Something we have known since 2002.
* https://cr.yp.to/djbdns/forgery.html
The DNS protocol is a terrible protocol. This report is not some novel discovery.