I really don't see why DNS records should be in the purview of the GDPR. I also think they are not public enough. It can be hard to contact people. Information is outdated, false or just hidden. Usually being able to call the person responsible for a domain and say hey your email server has relaying enabled and pushing out a lot spam gets them to fix it.
I can understand person not wanting to put their address, but I say phone, email, name and points contact should be necessary. It is a public system after all.
Spam can be a problem as well, but these records do serve a purpose. They also are important for ownership of a domain if a dispute was to arise.