Philosophically, I actually like the RPi approach (ie. a simple image with device tree) a lot more than ACPI/UEFI. ACPI involves a whole super privileged virtual machine with byte code from god knows where, whereas device tree gives more or less complete control over to the kernel image (sure PSCI is a thing, but that's a lot more defined WRT boundaries to me than ACPI).

Basically an ACPI system is a lot easier to bootstrap because you don't need to support all of the little subcomponents of the board explicitly, but once you supprt devoce tree, you support the board in a much more complete and meaningful way, and it's truly your kernel running the show.