What people don't really about the shaggs is that they were all trained musicians. They knew how to read and write sheet music and their musical style was, while still being outsider art, very much a calculated and deliberate effort.
This is completely and undeniably proven by the fact that all their songs are written as sheet music, with rhythmical and tonal quirks and all. And they can therefore reproduce it perfectly at will (and they have).
This means that they actually were beefhearts superiors.
As opposed to haphazardly trying until something works, the shaggs methodically composed their pieces as would a classical musician.
Truly geniuses of their time.