Yeah I think Linux does all of this plus has a UEFI stub. I'd like to see a low-level breakdown of what goes into going from kernel -> bootable ISO (that works on BIOS and UEFI).
An EFI program can exit and return control to the EFI shell. A kernel, however, makes an EFI call to terminate EFI services. After that, it can only call a tiny set of certain EFI functions, but the kernel is considered to have control of the machine. At that point, it will relocate itself from where EFI loaded it to where it wants to live, initialize new page tables, switch to those table, and proceed with its regular initialization.
The Linux EFI stub is a bunch bytes at the start of the kernel image that make it a legal EFI program.