Honestly, i am surprised but everyone who's not Adele/Bieber/1D/Taylor underperforms. Gaga declined, Ke$ha vanished, Demi declined, Beyonce isn't as good as she was with Single sales, Britney, Nicki, Iggy too. I'm actually worried for Katy now :\ The GP seems to get bored of artists quickly nowadays and want fresh artists.
Ariana started being huge two years ago, while Katy's been here since 2008.
honestly, i dont want to be shady, but in my opinion ariana has never had a good song. her music has always been without melodies.. so ofc after so and so many releases of the same ole formula the gp would finally see her for what she is...