Which, ironically, is evidence that "security through obscurity" does work, even though the authors implicitly criticize it in the same post.
How long did it take for Spectre and Meltdown to be discovered? Some vulnerabilities are easy to spot in an open design, but the more novel the exploit, the longer the vulnerability can hide in plain sight.
[1] On Intel, the IOMMU provides this. But just a cache that was aware of range-level protections (i.e. only allowed you to cache CPU-visible RAM from the CPU, etc...) would have worked.
This is like those Chinese outfits that laser off the part markings on ICs so others can't copy the design as easily. Eventually someone will find out what part number it is and the mitigation will be nullified. But it IS effective for a period.
In the same way obscurity provides a time bonus that must be worked through before exploitation can begin.
Hackers tend to complain very much about this obscurity stuff "all it does is waste people's time and it's not secure" which is exactly the point. Surely by now researchers must have realized that creating a 100 percent bulletproof security implementation is very unlikely when compared to how impenetrable any modern encryption system is, due to gotchas and flaws in the implementation details. And this is why obscurity slows down the discovery.
Denuvo DRM for new games is the same way. It is very hated but does work very well for the publisher at mitigating piracy for the initial 2-3weeks after a game launches where the bulk of sales happen.
The other reason obfuscation makes sense for DRM is the threat actors are individual consumers, who have limited time and resources to devote to untangling the obfuscation, and limited reward for doing so.
Normally we might expect to see many such users combining their resources to fund a solution to their problem at scale (by founding a public business or foundation for de-obfuscating DRM), but the state has made doing this punishable by prison. So DRM is rendered effective not so much through good engineering but through the legal system. This is an adequate solution for companies when the threat actors are simple civilians who want to play video games.
The issue with obscurity is that attackers inherintly have a far higher incentive to try and understand obfuscated, undocumented messes than security researchers.