How is writing your own music a marker of good pop? If a song is good, it's good, and if it's bad, it's bad, not only regardless of whether the person singing it wrote it themselves, but regardless of who wrote it at all. To me, it just seems like a silly standard that people approaching pop from other genres use to try to pick out the "tr00" artists. Considering the way pop as a genre works, you just can't break it down like that.
On which note, it's a laugh that people try and argue Gaga is a better pop artist than the bunch, among other reasons, because she wrote her own music. I don't care who fucking wrote it, it's still average at best, and so is she.