SOURCE
As you can see from this recently released chart, FourFiveSeconds is the 7th top selling song of the year
BUT, if you exclude songs not released during this year you'll have LMLYD by Ellie, SYA by Wiz and Charlie Puth and then again 45S.
Now, if you consider the fact that both LMLYD and SYA come from hugely blockbuster films and are strictly connected to the success of the films themselves and exclude them also, you'll stay with 45S only.
SO - 45S is 2015-released third best song and number 1 not considering Soundtrack Singles
and it's also the second general single by a female artist
SO WHY THE HELL ATRL THINKS IT IS A FLOP?