She did come close though, one of her songs was the second best selling song of 2015, world-wide. 

Its not exactly a ear worm..... and it doesnt sound like some dance pop thingy..

I dont think its going to set any records to be honest.
It probably wont be played that much or sell that much (talking out of my arse here).

I guess tastes differ but this song does nothing for me.

Gaga's "Perfect Illusion" for me! =)

Better than Swift yes, best song of the year no. For me the best song of the year is probably let the storm descent upon you by Avantasia.

 Is this a joke?

Not even remotely close, is a generic, empty, unoriginal and forgettable song, who can think this is the best song of the whole year? What kind of bubble do you live in?

'song of the year' LOL

the last super famous popstar I ever considered capable of making the best song of the year is Michael Jackson. It'll be a while before we get a popstar like him. Until then, the best song will probably be from a singer who's semi famous or completely unknown.

This year has been pretty garbage for Music.

We're talking sales? That's a different matter, I thought this was about the lyrics.

Music is not about the lyrics, that's like saying videogames are about stories.

Music is very subjective. Many metrics you can judge a single song by, some metrics matter to more people than others. I think we should give songs credit for their catchability and popularity, which are gauged by sales. I don't even know what Katy song was the second best selling one in 2015, I just remember glacing at some top selling lists and seeing her name there.