Not even close to being true. You can invoke syscalls directly, just needs a bit of reverse engineering. I wrote a bare metal libc library, with (not a whole lot of) effort I'm fully able to interface with the kernel/open windows etc. Fully statically linked, no libc, no win32, compiled on Linux executed on Windows.
The problem is this isn't really well documented _at all_, and I even ended up attempting to get in touch with the Windows kernel dev team to give me the actual internal syscalls/endpoints, but they refuse to cooperate. Which is why writing anything for Windows is entirely pointless.