"On the metal" is kind of a hazy concept on modern systems. If you write x64 assembler and run it on Windows/Linux, is that really "on the metal"? If you don't consider it to be, then you have a lot of work to do in getting it to boot with the screen turned on and a usable keyboard.

Whereas in emulating a complete old system like a BBC micro it is far easier to get to the metal while still being able to use the display and peripherals.

"Assembler" is really quite a portable skill once you've learnt at least two dialects, just as learning German and Latin will open most European languages to you.