The NT security descriptors are also so complex they are probably a little useless in practice too, because it's too hard to use correctly. On top of that the associated Win32 API is also too hard to use correctly to the point that I found an important bug in the usage model described in MSDN, meaning that the doc writer did not know how the function actually work (in tons of cases you probably don't hit this case, but if you start digging in all internal and external users, who knows what you could find...)

NT was full of good ideas but the execution is often quite poor.

Why inadequate (in the absolute)? This can be automated and let's encrypt allows verification through DNS, moreover this allows verification for wildcard certificates.

Now in this particular case maybe they should have gone through HTTP, and even automated with ACME. But there is nothing inadequate in the absolute in DNS verification. Besides allowing wildcard it also allows verification when you don't control the web server(s), when you don't even have a webserver at all, when the standard ports are occupied for something else, etc.

It was my understanding that MS now sign 3rd party kernel mode code, with quality requirements. In which case why did they fail to prevent this?

Disclaimer: I'm not found of web techs...