Barbra had one HUGE album, Guilty, and then all the others were only moderate selling and local, and appealed to an adult audience. She's sold so much Stateside because of her longevity and that mature audience, but she was never a 'huge pop girl' like we understand it today.
Donna only had one multi-Platinum album.
Diana Ross only had one big solo era.
Why do you all think Madonna is the Queen of Pop?

She changed the game for women. A female artist had never been so huge, so global, so dominant, so prolific in every area (hits, touring, selling albums, media exposure, venturing outside of her music field into film and business and fashion).