Well, the TianoCore EFI explains the boot loader part. But why you successfully can boot the 512b NVMe-drive without patching or injecting some drivers is a complete mystery to me. Or the boot process of apple is completely different from any other OS I know.
Did you patch your bootrom or how did you manage to boot from the NVMe-ssd? Or are you running a hackintosh?
It's a qemu virtual machine with real hardware passed though.
You know VT-x and VT-d.
Apple's still makes the best desktop OS, but Linux as far surpassed the macOS and Windows as far as taking advantage of modern hardware.
I haven't tried to boot Sierra from the NVME drive, as I want to use APSF and Sierra support is very limited, but I do boot from HS from it, and it works great. I have no need to go back to Sierra, everything works the same, but Apple seems to have dropped support of my old Firewire iSight. Tho that's OK because I haven't figured out the magic needed to pass a PCI FW card to qemu-system-x86_64 that OS X likes.
I did pass one to qemu-system-ppc and it works fine under OS 9 and Tiger.