I'm sorry but I could only stomach reading the first few pages of these comments. Rihanna will out last Katy?
I'd first like to take a few points others have made. Explain why they are wrong and then go onto explain my reasoning.
First of all, to the people saying Katy is "older" and the GP have a thing for young pop stars... this is my reaction:
To the people that say Katy doesn't experiment with her music..... I would like to ask you what on earth you think "Prism" is? Does anyone comprehend the artistic risk Katy took in releasing an album of (basically) ballads? There's not one stand alone "club" hit. In a world dominated by dance and EDM that's risk my friends.
Rihanna is a manufactured Pop star. She doesn't write her own music or create her own albums. She does what she's told when she's told and for the most part of it, it works. However the world is filled with examples of how young pop stars temporarily take over the world (like Rihanna has done) True longevity comes artistic integrity.
Katy writes her own music, she creates her own albums and she does that from personal experiences in her life. People will always connect more with something that's real and personal over something someone is told to sing about.
On top of that, Katy hasn't peaked early. She's gaining trajectory. Her career is only increasing and she's growing as an artist.