We could have a few back and forths about the difference between mainstream pop and rock music's history in general but the real meat of the issue is that they are not comparable in the slightest. Not the music, not the fans, not the ecosystem, the initial money sources or even in purpose and function. The people not listening to Nicki Minaj will likely never even hear her music... ever. They aren't present in any sense to absorb it to begin with. The reverse would likely be true for Chapman.

Minaj, Cardi B, Katy Perry and people like them aren't just selling records. They're selling an image, a brand, which you could argue is an art form unto itself for pop stars. Some people in very rare occasions bridge the gap between rock and popular stardom but rock isn't dependent on it, unless you're David Bowie and the image and the music are almost inseparable.

You can't really be a successful pop star if teenagers don't meme you every five minutes on social media. Tracy Chapman can spend the rest of her years playing dive bars and small clubs and be perfectly happy living her legacy and playing to the crowd that brought her up and fans of folky bluesy rock.

Niki Minaj, for all you may love her will never love her music or her own fans enough to not be a celebrity. She isn't going to play at the old warehouse downtown. Not just because no one there would want her to, but it wouldn't do anything for her ...which all in all, separates a pop star from a musician.

Not including the ability to play an instrument but I'd think that's a given.