This isn't saying that they're all copying her, it's simply saying that there was a craze for different after her. And its true, everyone was trying to be different after her
Yesterday I made this post and I know that is not to attack other artists, it was just a post of how Gaga has influenced other contemporary artists. NOT REQUIRED TO PERFECTION AND IDENTITY YES! WITHOUT PREJUDICE
Katy was different before Gaga ("One Of The Boys" cover art) . It's the same for Avril (please she was an emo in 2006). And maybe you should watch "Disturbia" of Rihanna (2008) before talking about her.
i think its a bit unfair to say that everyone is copying gaga now. however, i think she definately changed the celebrity world, so its not that theyre copying her, just following fashion trends that gaga may have initiated.