Sure, Miley Cyrus is one of the great media stars of the decade. But when it comes to her status as a hitmaker, she is an upstart compared to icons like Rihanna, Lady Gaga, Usher or the legions of greats that came before them.
She should just change her actual name at this point.
Read and learn to interpret the graph. This graph is about hit songs and nothing more, and we all know Rihanna is the queen of hit songs. This has nothing to do with who's "bigger".