[Koshkin]

I wouldn't call "niche" something some big companies have been spending billions of dollars on.

[ogogmad]

In module theory, which is a bit close to ZX, category theory gets used in a big way to calculate things: See left/right exact functors, co/contravariant functors, derived functors, the hom-tensor adjunction, etc.

But!! I'm not seeing ANY of that in ZX.