Now prioratizing unambiguos naming would be somewhat acceptable if ICANN was tacobell and just a steward of naming on the side.
If you are not a consumer on an ISP emulating dialup it is quite likely that a popular name in a naming convention I.e. 'mercury' resolves to something for you and something for someone at a different firm (mercury.intranet.[firm].not-so-stupid-tld). A cert is possibly not a fully qualified one so when ICANN gives away mercury you need to append .asshat to everything ICANN names.
(Two firms have an unambiguous situation because they don't trust each others private roots but they both trust a cert issued for the public trust as a fqdn which is why TLDs expanding is a form of theft/breakage against every intranet..)
The DNS naming confusion was largely dealt with by having a small number of TLDs and rarely referring to complex things like partially specified subdomains, but every once in a while a fool named their machine com, org, or net. (Though these as subdomains were far more toxic.)
There is the argument that ICANN should no longer be consulted ever by nodes of consequence but that is an argument that they have failed 100% in their responsibilities.
If you don't care at all about zone delegation and global resolution then you obviously don't have an opinion on how to evaluate ICANNs stewardship of global domain delegation.
We have run out if IPv4 addresses but there is NAT is not a satisfying answer to start. But we have let ICANN polute naming so let's implement shadow naming everywhere is an even less satisfactory answer.
If I understand correctly, the scenario is an internal machine named "george", which is being properly search-pathed and looked up as "george.example.org." with nothing leaking anywhere, becoming vulnerable to Walmart being able to issue certificates in the name "george", because the DNS client library's search pathing is not read out by the layers that simply know the machine as "george".
I'm not totally convinced by the premise here that certificate checkers never read out the final fully-qualified domain name from getaddrinfo().
HN is full of people from SaaS startups who in essence want to buy the perfect 900 number. But DNS and delegation goes far deeper than selling one name for $20 and going to other $20 names to store your code and email at other SaaS providers.
As for certs, AFAIK, you can't get a certificate for a non-fqdn from a public CA since 2015.