although I disagree with the "everything has been done before" mindset, that wasnt the point.
the point is her quarelling with Perry over this matter is lame given her own career choices
Everything pretty much has been done. Not saying all artists explicitly rip off others, but they are influenced by others in some way and that usually shows through their work in some way, whether it be doing a similar style of choreography, clothing, music, etc. I don't remember the last pop artist where I thought wow, this is totally and 100% something brand new that I've never encountered before.
I think gaga's excuse is that hers is homage while she feels Katy is just ripping her off. I can kinda see how for gaga there's a difference, even if I disagree.