Clarence Reid ushered in the Miami sound (KC and the Sunshine Band and others), he also ushered in X-rated rap in the 70s.
So disco and rap (even in excess) have linked origins. And every big name rapper knows “Blowfly” (Clarence’s alter ego), they listened to their parents’ dirty records when they weren’t home.
Lots of things are linked. Doesn’t make all bad.
The feel of the music is completely different. Disco is a smooth groove eminently danceable, and included couples dance again. Rap is just monotonous evil.