You're right that re-flashing firmware is a bit of a minefield. You have to really pedantic and follow the manufacturer's instructions exactly to the letter.
I differ slightly on the idiot proof comment though. I don't know how many systems I've flashed over the years, but it's many.
As a retired software developer, I expect the manufacturer to include the model/version number in the new firmware, then the firmware on the device will compare it to the system itself, possibly warning you you're trying to flash the wrong firmware or the firmware version on the system is newer than the one you;'re trying to flash.
Unfortunately, some manufactures just 'bung it in' and if it crashes, tough luck. For a system that allows end users to do firmware updates, I consider this sloppy and would expect something a bit more thorough.
But as I say, there will often be a method of getting it off it's knees. The units are probably manufactured as being completely blank or bricked, then the firmware will be loaded and it all works. The question is, can we find out that process and get the right firmware in?
Just my two-pennorth 😁