MIDI is a protocol for describing audio.
Sure, it saves a lot of bytes compared to PCM encoded wave-form data, but it's not really cheating anything unless we also consider the red, blue and green parts of the computer monitor to be cheating because we're not outputting colours as raw wavelengths, but instead the monitor is decoding compressed signals into actual colours.
What is this "cheating" you speak of? I wasn't expressing any judgement, just saying that using MIDI helps save bytes. But now that you mention it, the bitmapped graphics that we take for granted nowadays also help (it gives you a whole memory space to work with that doesn't count towards the length of your program, rather than having to "race the beam" -https://en.wikipedia.org/wiki/Racing_the_Beam). Not sure if there's a demoscene for the Atari 2600, but that would probably be the most "bare-metal" you could get...