@p >If the kernel doesn't respond to syscalls, nothing happens.
If GNUboot doesn't init the hardware and then launch the GNU GRUB OS on my computer and then launch GNU Linux-libre and then launch the init and then launch the rest of the GNU and other software, nothing happens.

Of course you can boot Hurd from GRUB instead just fine and the Church of Emacs runs just as well.

>it emulates the interfaces well enough that it runs Unix software from the 1970s
Any of such interfaces have been implemented by GNU and not Linux.

In this case, printf() is a function implemented by glibc, not Linux.

>it does not present a Unix interface to the software it runs?
If you try to pass a proprietary binary compiled for a Unix to Linux via a loader, Linux won't be able to make any sense of it, as it does not re-implement *any* Unix interface - it implements its own custom interfaces.

The thing that presents an interface to software is GNU, although in certain cases the programmer can decide to interface directly with Linux's non-Unix SYSCALL interface.

>you are trying to make the case that it is not a complete operating system
It is a FACT that Linux is only a kernel and is certainly not a complete operating system, but many people don't want the facts to get in the way of their proprietary dreams.