I don't know why Xtina was left out. She co-writes 90% of her music, can sing her ass off, and knows how to command a stage without dancing, but can do that when she wants, too.
Britney: It depends if you look now or back then. But as of now.
Vocals:4
Dancing: 6
Songwriting:I don't know if she writes her stuff, but I'll give her a 6
Performing: 7
=23
Katy Perry:
Vocals:5
Dancing:0 (never saw her dance)
Songwriting:6
Performing:4
=15
Rihanna:
Vocals:6
Dancing:3 (I don't see her dance a lot live, but I can remember her "dancing" in some videos)
Songwriting:7
Performing:7
=23
The songwriting part is kinda subjective for me - I only know that Gaga write almost 100% of her songs but don't really know about the other artists.
I would say any deviation on vocals from Beyonce>Gaga>Rihanna>Katy>Britney is pretty delusional.
For dancing Britney=Beyonce>Gaga>Rihanna>Katy.
Songwriting is behind closed doors so we don't really know. The truth being Gaga>The Rest.
And performing is subjective.
...There are other huge factors of being a pop star talent though. Personality, diversity, creativity, commercial appeal and promiscuity all come into play. Katy has by far the highest widespread commercial appeal for example, whilst Rihanna is extremely diverse, Britney is extremely promiscuous/sexy and Gaga is extremely creative. Also things like the ability to be likeable, trendy and "cool" are important.
What i don't understand is people giving beyonce low scores for "songwriting" and then high scores to rihanna when rihanna didn't co-write or write a single song on "loud". That ALONE puts her below everyone else on songwriting.