katy didn't destroy GAGA, to destroy her she had to overcome her and be a step ahead of her something she didn't even accomplish with her biggest effort Teenage Dream, yes Prism had more success than Artpop but that doesn't mean anything when we take into consideration everything Gaga was able to accomplish and conquer. Gaga's ego destroyed her.
Katy's a fly flying around a dead body, she's still alive but just an insignificant fly that will vanish very soon (flies only live one day after all)
