If you want pure Assembly in binary libraries in C++ and C#, Visual Studio can also display them, one just needs to select the right options.
Indeed it only shows disassembly. I was frustrated that VS wouldn't even show me that. Others write that newer VS lets you enable the showing of assembly.
Anyway, I am spoiled by Java, where I can step into standard library code (which is in Java), can decompile to produce pretty nice Java source where the source is not available, and IntelliJ, which automatically downloads the source where it is publicly available. It's quite wonderful. But I am guessing you already know this, judging from your profile.
To me, not being beholden to documentation is an incredible freedom. The ability to just pop open the source to understand the tool you're working with is indispensable once you've experience that freedom. Microsoft developers don't have this ability, and having had it, it's hard to imagine being without.
ILSpy and Reflector are almost as old as .NET itself.
Visual Studio always had an Assembly view since version 1.0, and there is always WinDbg as alternative, including macro commands to dump .NET JIT information.
Sorry, but it looks like that you haven't properly explored Windows development.