The Pi is really a GPU with a CPU added on so the whole system needs to be brought up by the (binary blobs for running the) GPU. Hopefully not the case in these more PC-like systems...

Huh? Never got deep into it, but always thought it was some kind of arm cpu with underpowered integrated gpu or similar.

It’s actually a GPU that handles initial stages of booting, through some closed-source firmware blob.

Bootloader doesn't count?