Earlier quoted context omitted.
> only a small minority of the processes running on an OS X system. Which are anyway not POSIX. https://www.amazon.de/MAC-OS-Internals-Amit-Singh/dp/0321278...
POSIX is an application interface. How OS X is implemented under the hood is irrelevant. It does present an application interface mostly conformant to POSIX standards, so it is some way POSIX.
That's hardly encouraging, when all the basics and all the newer OS X abstractions are based things other than POSIX standards, and ask programmers to connect to them with non-POSIX interfaces.
The fact that it also supports a POSIX layer is about as relevant to what we're discussing (whether POSIX is fit for today's needs and used in today's mainstream development) as the presence of some X Windows translation layer is in Wayland.