Unix is easier to understand than the NT mess and everything it's in the open and documented, so you can achieve a good level of knowledge in the middle. OTOH in order to understand NT deeply you must be a reverse engineer. Also, on the other side, crazy experts under Wine (both ways, Unix and NT) OpenBSD and 9front do exist on par of these NT wizards. It just happen with Unix/9f you climb an almost flat slope (more in the second) due to the crazy simple design, while with NT the knowledge it's damn expensive to earn.

With 9front you OFC need expertise on par of NT but without far less efforth. The books (9intro), the papers, CSP for concurrency... it's all there, there's no magic, you don't need ollyDBG or an NT object explorer to understand OLE and COM for instance.

RE 9front? Maybe on issues while debugging, because the rest it's at /sys/src, and if something happens you just point Acid under Acme to go straight to the offending source line. The man pages cover everything. Drivers are 200x smaller and more understandable than both NT and Unix. Meanwhile to do that under NT you must almost be able to design an ISA by yourself and some trivial compiler/interpreter/OS for it, because there's no open code for anything. And no, Wine is not a reference, but a reimplementation.

That's kinda true for older/integrated parts of Windows, lots and lots of functionality that people have come to rely on over the years, but also huge black-boxes that you need to not be intimidated at probing into to solve weird issues (that often becomes understandable if you have enough experience as a developer to interpret what the API surface tells about the possible internal implementation).