I don’t think this is true. Instrumentals in hip-hop are largely first class citizens. Lyrics are at the forefront, yes, but consider that rappers are judged more on their technical ability to navigate the beats they choose.
It’s the only genre where artists are regularly deemed unworthy of their own instrumentals.
The author’s example is ironically the best example of this. It’s N.Y State of Mind by Nas (regarded as one of the best beat selectors of all time), on Illmatic (one of the best hip-hop albums of all time), and produced by DJ Premier (one of the best producers of all time).