In the age of hip-hop, female pop stars are facing an identity crisis.

In July, R&B/hip-hop surpassed rock for the first time to officially become the biggest music genre in America, according to Nielsen Music, which tracks online streams and digital and physical albums. As of Oct. 12, R&B/hip-hop has driven 24% of music consumption in 2017—more than rock’s 21% and double pop’s 12% share.

So...