Let me just say that I bought Problem the first day it came out, but I've legit never bought anything else from Ariana. That song was 1) a chance to dethrone Happy 2) a really great song 3) a great offering from such a relatively new artist. Ariana doesn't do much for me at all and I haven't been a supporter since that purchase
I'm not saying Problem is a fluke, but I wouldn't use it as a measure of Ariana's overall popularity. Between that and donutgate, she still needs to be PUNCHING and getting more people on her side. Focus was a huge misstep, when she clearly needed to show the public a new side of her. Her place is not solidified and it seems like they got complacent.