Taylor is a bigger touring force
Taylor is a bigger album selling force
Taylor has won the biggest Grammy (and does not need to rely on other people to win the smaller ones)
Taylor has even sold more singles in the most important market (US)
Right now, RIhanna is just marginally bigger. When you convert TEAs/SEAs, Rihanna is still above Taylor. Taylor will easily surpass Rihanna with her next album, though.