[JdeBP]

> read that: at all

And that's the point where you went wrong. (-:

It is wrong to assert that Windows NT has no message passing "at all".

The original design of Windows NT had applications opening LPC connections to a server process, the Client-Server Runtime SubSystem, and sending it messages for many API calls. Although the graphics system has since moved into the kernel and then partly moved back out again, some of this application-mode message passing to a CSRSS server process remains in Windows NT even to this day. All interaction with the LSASS is also client-server application-mode message passing.

And there is a lot of message passing inside the kernel. The entire I/O subsystem involves passing around IORPs, which are messages.