Katy has
power in music, she's a force, those first week sales mean nothing lol

Outside of music, she's obviously not a big celebrity name like Jennifer Lopez or Beyonce but that's because she primarily focuses on her music.
People will rembember her, her bright, empowering, fun songs. Katy's young fanbase is actually her advantage and they won't forget her/her songs in the next 5-10 years. I'm sure she'll outlast Gaga, Miley etc.