ATRL logic dictates that a "main pop girl" is a pop girl who is currently successful, so going by that logic:
Taylor (successful album)
Katy (successful tour)
Gaga (just ended successful tour, successful album, about to start another successful tour)
Beyonce (made more money last year than the others)
Meghan Trainor (two hit songs in the top ten)
Iggy (a couple of hit songs)
Ariana (a couple of hit songs)
By ATRL logic, Rihanna isn't a "main pop girl" anymore because the last successful thing she did was a collaboration. I can't say I agree with that logic, but ATRL can't be hypocritical about how it labels "main pop girls". Adele is also hit by this logic, but you could argue that the success of "21" will make her a "main pop girl" for the rest of her career.
Gaga isn't a MAIN pop girl anymore. She has quit making pop music and she wasn't nearly as successful as her peers (Bey, Rih, Tay, Katy, Adele) with her last release, even being outsold by Miley Cyrus. Despite the MASSIVE promo and a big budget video, GUY only peaked at #76 on the Hot 100, being outpeaked by songs like Rihanna's Right Now (which had no music video and charted solely because of airplay) and Loveeeeeee Song (which wasn't even released as a single). She lost a lot of buzz as people don't seem to talk about her as much either.
Gaga isn't a MAIN pop girl anymore. She has quit making pop music and she wasn't nearly as successful as her peers (Bey, Rih, Tay, Katy, Adele) with her last release, even being outsold by Miley Cyrus. Despite the MASSIVE promo and a big budget video, GUY only peaked at #76 on the Hot 100, being outpeaked by songs like Rihanna's Right Now (which had no music video and charted solely because of airplay) and Loveeeeeee Song (which wasn't even released as a single). She lost a lot of buzz as people don't seem to talk about her as much either.
No one knows about Mo, Charli, Becky or FKA twigs. 
