It would mean that Katy isn't a singles artist and can sell albums? Now if Kesha outsold Gaga then she would be over. But neither of those 2 things will happen.
Depending on the sales numbers it could mean that Katy is selling well and obviously that people like the album more.
Gaga won't be over soon, even if she'll become a niche artist. It wouldn't matter, because she will continue to release the music she wants to release and we'll see who likes it. Same goes for some other pop girls, but they always have the option of adopting another strategy and making more mainstream music. I'd rather Gaga's popularity dwindles and stays true to herself than that she starts making music she hates but the people will eat up
I don't understand if he OP is trying to shade Gaga or Katy
I think it's unintentional shade for Gaga. He obviously thinks that Gaga is the biggest pop girl and is asking if Katy outsold her, would that mean that Gaga is no longer the most successful pop girl? (I don't think she's the most successful pop girl).
, Britney's, Taylor Swift's (outside the US), Justin Bieber's, etc careers are all over. 
