I think Taylor overanalyses things and reads into stuff way too much. Katy probably didn't have the time to become one of her BFFs and text her non-stop, so then when her dancers went back to her, she probably thought "Katy hates me" and when Katy and John started a relationship, she probably thought "Katy hates me" and when Kanye West featured on the E.T. remix she probably thought "Katy hates me."
I think it would have been wiser and classier to just settle it behind the scenes rather than throw someone under the bus in a song. I know Taylor communicates her feelings through song, but if she wanted to do it, she should have kept it anonymous. I kind of think letting the public/media know it's about Katy makes it a bit of a diss track, and that's just not classy.
I really hope the two of them can settle it over a mature phone conversation to explain their respective perspectives to each other