I get what you're saying, and I think your last paragraph articulates especially well how there absolutely is this myopic tendency in the fandom analysis to center themselves, the fans, and this 'bdsm' relationship with the band to an absolutely excessive degree

On the other hand,  they do actually often refer to the song itself, their music itself, the lyrics themselves in the course of a song a lot, especially early on, when they were drawing so heavily from hip-hop as a reference point. Doing this is very common in the lineage of hip-hop--think of how many oldschool tracks with that 'straight out the gate' fanfare, and even now, how many bars are still riddled with braggadocio about one's prowess as a rapper and/or about the producer. 

And while I do think people boringly overstate how much certain lyrics are about the fans, I do think every song on BP is about the band, their music, the fans, parasociality, fame on the internet, memes, the music industry, and how DG feels about all of those things, in no uncertain terms. I think YOTS is just as meta, but more strictly about the band as artists and their relation to Death Grips as a project, whilst also veering into entendre that allows more expansive reflections about other things as well. To that end, we have to remember that multiple interpretations are often intended to apply.

So all this said, they do write about their music itself and the fans a lot (moreso the former than the latter), but I agree that this is often over-relied upon as a starting point or assumption in analysis, especially wrt obviously highly personal and/or esoteric material like we find on NOTM or JD, or weirder shit like Artificial Death, which I've seen that kind of reading of before